CV Carburetors, overhaul, etc., Part 1 of 2 parts
There is no specific article on this website for Airhead "slide" carburetors; only the articles for the "CV" carburetors.
ALL of the Bing carburetors, with STOCK floats, which means the 1/26 models as well as the 32 and 64 series, have a specification for brand-new floats, of 10 grams. After they have been in use, they MAY get heavier. About 13.5 grams is near the maximum. For those with gunpowder or other scales, weighing in grains, 200 grains is about the limit.
2014, R. Fleischer
basic mini-overhaul can be done with the carburetors in
place on the engine.
Quite frankly, this is often
READ Article #6 on the R75/5
carbs....some really IS pertinent to all the CV carbs:
READ: http://bmwmotorcycletech.info/bingcv-2.htm That is Part 2 of the article you are reading now.
For a well-done article...step by step...with 44
pictures....see BMWMOA magazine, BMW-ON (BMW Owners News),
for March 2003, for an article...in great depth...by Gary
L. Smith. You can probably get that back issue
From that main page, click on left side for Country
Store, and then on the Country Store page, go to Back
I have SOME nitpicking on that article:
1. See my notes in the article you are reading.
2. Use faint amount of silicone grease on all O-rings
and on enrichener parts (do NOT overdo this, you do NOT
want to plug jet holes).
3. If doing a complete overhaul, which involves
removing the butterfly to replace the throttle shaft O-ring
(be sure to silicone grease that one too!), be SURE to MARK
the butterfly for correct refitting: something like
TOP, OUTER; or TOP, facing REAR...or something of that
sort....BEFORE you remove the old one. You can hope that the previous workman did not install yours backwards, because it can be fun to figure out unless you know what it is supposed to look like. I ADDED, in the article you are now reading, on 05/14/2012, photos of what it is supposed to look like, and NOT look like.
4. The article you are reading will have more
complete information about orienting the enrichener parts.
Below is a website in which you can enter your carburetor
model number, and get a chart showing all the component
The Bing CV carburetors are moderately complicated in HOW THEY WORK. BUT, there are only a moderate number of places in these carburetors where you probably could run into trouble. For the 'Newbie', I advise reading all of the carburetor articles completely through, even though you will not likely understand everything at first read. Once you have overhauled your first Bing CV carburetor, you will probably wonder what all the fuss was about.
NOTE: The float needle tips
tend to get faint grooves in them after a lot of miles, and, if a rubber-tipped type,
the tip "rubber" material gets slightly harder, and (modern gasohol especially)
deteriorates them, and then the needle
tip does not seal well, causing the bowl to overflow onto
your foot. This can also happen if a TEENY particle
of dirt gets into that float tip and mating seat area, and
also if the float deteriorates enough. The
stock float and float needle probably should be replaced
every 30,000 miles. It is VERY common to see a carburetor overflowing onto your boot. Most Airhead owners have had the problem at one time or another. The fast fix is to turn off the fuel petcock(s), remove a bowl, and jiggle the float up and down with the fuel ON, to flush out any particulate matter in the float needle-seat area. It is important to keep the fuel tank clean, and as they age, the interior reddish-brown lining deteriorates, clogs screens, etc. Use of aftermarket fuel filter(s) below the petcocks is almost a necessity now, with the aging bikes. Information on screens, filters, updates, etc., is elsewhere's on this website.
NOTE: Except for the earliest carburetors with no plunger on the float needle (no rubber tip on the needle either), if you left the teeny clip off the float needle and float, the chances are that the float system will work just as it is supposed to. You COULD, however, have a situation where the needle ‘stuck’ to the needle seat, and no gas flowed. FYI, I used to purchase these wire clips about a dozen at a time, and I used to need one every few months when I had the shop. It is ever so easy to have one flip someplace while trying to install or remove. I used a 3 power magnifier on my eyeglasses, and always did the work on a piece of old white bed sheet! I tried magnets, some help, sometimes not.
On the EARLIEST carbs, the needle was all-metal. Bing had some problems and made several changes, approximately at the same time. The needle was changed to some sort of rubber-tipped type; the needle lower end was drilled, the needle got an internal spring loaded-plunger with a teeny hole at the bottom end, on the side, and the clip was installed. I believe that Bing incorporated the spring loaded plunger so that the fuel level sensing was more accurate, and so the needle would wear LESS, as less pressure was needed to close the orifice off, but more was available. That is, the LEVERAGE is such that as the fuel level rises, the pressure on the seat increases rapidly, compared to a very small fuel level increase. This is difficult to see, and a nerdy point anyway.
I believe that as the plunger tip wears, which it does and the wear shows as a ring, the needle, being loose-enough in the vertical well area it fits up into, could cant sideways a bit. That MIGHT allow the grooved fuel shutoff needle to hang-up ever so slightly in the SEAT. Since only the needle weight, plus weight of fuel, and maybe vibration, etc., is going to be moving the needle downwards to let fuel in, Bing incorporated the clip, so as the float assembly went down as fuel level dropped, the float assembly positively pulled the needle off the seat.
NOTE: Replacement of a float needle SEAT is rarely needed. Detailed information is here: http://bmwmotorcycletech.info/bingcv-2.htm
the floats, my testing, information on failures, alcohol
in fuels, etc.
This is a LONG section, and is here for reference purposes.
The stock dual 'one-piece' plastic float assembly does not
always fail by getting considerably heavier; yet when bad,
it will sink in
gasoline (essentially hardly any will be above the surface
in a container of gasoline in which the float, without pin
or anything else, is trying to float). Once it deteriorates
and begins to sink,
your mileage will get worse and worse, eventually perhaps
flowing onto your foot.
Floats are not consistent in how
they fail, and that MAY be due to the type of gasoline they
are used with. New floats weigh about 10-13
grams. A horrendous badly sinking old float that
almost sunk totally was measured at 18 grams. MOST stock
white one-piece floats will get heavier as they
deteriorate. Once they are removed from
gasoline and very thoroughly dried, which can take a lot of
time, they may lighten considerably, and then not gain much
weight if again put back into gasoline....at least for a
month or two period of time for drying.
The reason for the floats failing
even when they weigh less is not well understood. It SEEMS to be
a shift in mass, and the outside dimensions do NOT hardly
change. Remember that this does not always
happen, and the floats mostly fail by increasing their
weight. The floating
test is the only good test. This simple test will be explained later in this article.
Information from extensive testing on a large number of floats was FINALLY! completed, after many
months, on July 13th, 2003. I had accumulated a
goodly quantity of used Bing plastic 'one-piece-assembly'
floats, for which I hereby give special thanks to all those
who sent them to me. These floats came from both slide and
CV Bing carburetors, some were very old indeed, and others
not very old at all. Testing took quite a few months. Since
the floats were WELL dried out when I received them (At
hardly understood a problem THAT brought about), I had to take measurements of various sorts and
then put them in sealed glass containers with various
fluids, and let them soak at least a month, and then retake
many measurements. Weight was a primary concern, but I was
also interested in mass, distribution of the weight/mass,
dimensional changes, etc.
There were some surprises. I had
EXPECTED to find that some solvents would actually start
visibly destroying the floats, but this did NOT happen. All
sorts of liquid solvents were used, many of
which were known ingredients in gasoline's from across the
country. I obtained samples of gasoline free of alcohols,
free of MTBE, free of ETBE....etc....as well as gasoline's
WITH those additives. I did testing of the floats in
specific liquids/chemicals. I also did some testing by
MIXING various chemicals/solvents, as just putting floats
into a single solvent is not, theoretically, adequate to
establish all possibilities.
I hardly think I exhausted all the
A bit of background follows, then the float testing
Alcohol, ETC: Some additives are used as 'co-solvents',
that is, adding them ALLOWS other additives to MIX with the
gasoline, that might not mix by themselves.
Yes, this allows WATER to mix with the gasoline, among
other things. Some additives are used mainly
for oxygenation purposes. Theoretically, under
some conditions, adding something that contains more USABLE
oxygen, per unit of volume (or weight) will allow a fuller
burning of the fuel. Under SOME government
mandated test routines, they lower the 'smog' output of the
engine, BUT, they USUALLY cause a DROP in mileage, causing
more smog from just that alone. SOME types of emissions ARE actually increased per mile
traveled...they are just not the one's the government
agencies have a priority on. Use of
alcohol (and several other additives) containing fuels will
almost always result in a LEANER burning condition,
generally meaning higher engine temperatures, and if
severe, can lead to burning up pistons, problems with the
valves, and even engine seizure. While it
is true that alcohol has a higher octane equivalency,
using alcohol requires
more VOLUME of alcohol. In order to
maintain more consistent burning, one really should change
one's jetting (needle and main jet) to slightly RICHER,
if alcohol fuels were used all the time, and the
fuels were consistent in formula. This would REDUCE gas mileage even more than such fuels do
with the stock jettings, although driveability would be a
bit enhanced. ONE step at the needle JET (NOT one step of the needle clip!) is usually enough, plus 5 or 10 digits on the main jet.
Use of alcohol fuels is, in my mind, should be absolutely forbidden
in PREMIX type of 2-stroke engines, as the alcohol and
water can separate out of the oil, and the engine seize
from lack of lubrication. In the Airheads, it is not a big
problem at up to 10%, but alcohol CAN cause 'driveability
problems'....poor throttle response, hiccuping, jerking,
lousy warmup. If your bike is already lean running, and
Airheads from the 1980's, especially those exported to the
U.S. are like that, you might have WORSE driveability
problems....or...overheating. Testing for alcohol can be
done rather simply, but it is a PIA to do at every fillup,
and this type of testing (mixing in a test tube, with
water, see if water level rises) also will, unfortunately
(or fortunately??) show up MTBE,
and some other additives that absorb water. California's
reformulated gasoline's are a problem, and this has spread
to other States, although California has now phased
out MTBE in every part of the State due to its disastrous
effects, if spilled, on underground water supplies.
Alcohol-laced fuel is now STANDARD in the USA, and it is typically difficult to find alcohol-free fuel, and when you do, it is $$$.
Some States require labeling the pumps, some do not, some
only if the % of alcohol or ??...is at some particular
level or beyond.
There are THREE common types of
alcohol, isopropyl (rubbing alcohol), ethanol (drinking or
corn) and methanol (sometimes called wood alcohol since
that was one way of making it, nowadays it is made from
natural gas; and, it is very poisonous and quite
corrosive). Generally speaking, methanol can cause
corrosion of aluminum, can be hard on rubber and plastic
parts...and brass parts. THAT covers just about everything
in your airhead's carburetors but the steel pin, needle
and the diaphragm, and those can be affected with water in
the mix. Other additives are not great either: ketones,
ethers, etc. Common 'gasohol' has 10% alcohol, but may
contain LOTS of other 'things'. The alcohol in gasohol
will raise the octane, but leans the mixture in the bike, which is why
most FI cars can get away with using it (at a cost in
mileage and some in power), but many older carbureted
vehicles will not like it. The better of the alcohols
is isopropyl, it tends not to separate out, and is fairly
stable. Isopropyl, however, is not the alcohol of choice of
the vested interests that grow or sell corn or the
politicians who have, well, interests in this area.
It is hard to give solid recommendations on storage of
today's gasoline's. Generally, with the use of
a product like Stabil, a few months is the best one can
hope for. It is better to clean and then dry out
the system, including the tank. In fact, cleaning
the fuel tank thoroughly should already be on your
Because of the horrible additives used in gasoline's today,
gasoline can NOT be stored as long as it used to be, not
even with an additive you purchase such as StaBil, although
it does help. The
gasoline will deteriorate, not good for tanks, petcocks,
hoses, and, of course, the carburetors. It tends to gum up
during that deterioration.
A product often called 'dry gas' is sold to car owners in
wintry States, as it, an alcohol...usually methanol or
isopropyl, mixes with water at the bottom of the tank, and
in fuel lines, enabling the water to be 'burned' ...so to
speak. Adding that product MIGHT increase the alcohol and
water content of the gasoline to a critical level...causing a separation process...and water and
alcohol will now be at the bottom of the tank, rotting out
the tank....or, worse with a premix two-stroke
engine, the oil could separate out, and the engine would
not get lubricated.
Types of liquids I tested:
isopropyl alcohol, high % as well as mixed with water.
ethanol....medium %, as well as 154 and 191 proof..
above with varying water content as well as chemically dry
California MTBE gasoline.
Known standardized Chevron 91 octane fuel.
California reformulated alcohol added Gasohol.
a solvent consisting of a light aliphatic complex with
naptha's, toluene, xylene, methanol, acetone and MEK.
common denatured alcohol.
MTBE high concentration.
a solvent consisting of toluene, n-butyl acetate,
2-butoxyethyl acetate, and a few other things.
RESULTS OF ALL MY ABOVE TESTING:
I. Weight change (weight is in 'grains'; there are 15.43
grains per gram):
Used floats tended to be in
the range of 185-255 grains when well
dried out. After soaking for weeks in various
chemicals/solvents/gasolines, one particularly bad set of
floats was almost 262 grains immediately after removal from
MTBE containing gasoline (allowing a couple of minutes to
evaporate the surface liquid). This was a very bad set
indeed. But this set was 255 as I received it. This
means that whatever change happened to these floats, it was
mostly permanent. Typically the weight change
occurred during the use on the motorcycle, with only some
more moderate increase when put in the various liquids.
This suggests that the aging is very slow. MTBE
is only ONE of many harmful substances. MTBE has been phased-out, due to water table contamination.
***I should note here that some folks
sent me information on weights that I could not duplicate.
I was rather suspicious, and then I made an interesting
discovery. If a float was never dried out thoroughly from
first being put into service, UNTIL removed and replaced, and
then sent to me, then the weights might tend more to agree
with information I was given, as those weights were taken
right after removal. My conclusion was that it
is likely that the first (since brand new) and constant
immersion in fuel changes the float in weight/mass movement
vastly more on a percentage
basis, than after the float is dried out from some years of
being in service, and re-placed into gasoline.
This might show up as a smaller effect if my testing had
gone on for MANY months in the various liquids.
MIGHT. I was a bit intrigued by this
idea. I did some experimenting with cutting open and
drying, a few float assemblies, but NOT loosing any of the
material...and it appears that my hypothesis may well be
correct. While someone could compensate their floats
for this effect (by measuring actual depth in the float
bowl and adjusting for that....AFTER drying the floats
really well after long usage....it is a moot point, as I do
not really recommend this. Saying this
all a bit differently: it APPEARS that a brand new
float, once put into gasoline and kept in gasoline (except
perhaps for very short periods allowable without
gasoline...such as carb bowls off, perhaps for a day's
overhaul), changes internally, and that internal change is
permanent...or if not, it takes a VERY long time for the
change to revert any.
II. Some special tests were made to determine if there was
a shift in the concentration of mass. This WAS found to be
so. This was not excessive, but combined with an over-all
change in weight, was more prominent than might be
expected. A small change in mass movement, plus a
small change in weight, would be enough to cause a float to
sink a fair amount.
III. Change in dimensions: of each float assembly, both
sides were measured for width and length. There was a small
variation noted even with brand new floats. One surprise
was that the dimensions changed very little from
new. I theorize that the outside of the float
tends to harden some, and become slowly more impervious,
whilst the nastier fuel components get inside and do their
damaging work on the float inner portion.
IV. Other changes: INternal discoloration was NOT noted on
some, but the worst were ALWAYS discolored.
Almost no truly bad reported (by sinking noted by owner)
floats were still white on the outside (although some were
INternally a bit darker).
ONE SPECIAL THING WAS NOTED!! As the floats became
worse....that is, they tended to sink in gasoline more and
more...and usually became heavier.....the INside of the
floats tended to turn into a somewhat MUSHY and almost
granular mixture, even if left out to dry for a
considerable period of time. ONCE cut open, they
would dry out, although this took a fair amount of time...several
hours, and not fully for a few days. The OUTside
tended to be a harder 'shell'. The conclusion is that
whatever the exposure medium was, it tended to migrate
INside and make changes to the contents, and generally
INcreased the internal mass weight. Mushiness
and granularity was not the only change noted!...there was
a small shift...mass movement to change the CG! The worst
floats tended to have small voids in the floats (bubbles or
similar). My suspicions are that something...perhaps
something in gasoline I did not test for....may be
modifying the insides of those floats, besides the fuels
tested. It is also possible that the initial brand new
float change to the interior is actually the effect of the
things I tested for, but would take many many months.
There was absolutely no doubt that MTBE containing gasoline
made the interior of the floats mushy.....but surprisingly,
since Bing touts its dual-independent floats as
'alcohol-proof', I did not find big changes with alcohols
of any common type! My suspicions are that some dyes
may be at work here too. Again, other things besides
MTBE are suspected by me of causing the interior changes.
managed to obtain a float and do some retesting during the
late Summer and Autumn, of 2005. This time, I
measured only weight, and the only liquids being tested
with the floats, after a couple weeks of soaking, were hi
proof ethanol; anhydrous methanol; and a refinery product
of mixed solvents/items, that I obtained from a refinery
worker....this type of mixed solvent is a byproduct,
generally, and is often mixed into batches of motor fuels,
to get rid of it...and for?? reasons. Also, in this
particular series of tests, only the SAME float assembly
was used, thereby exposing it to a series of
solvents. The float assembly started out as 197.2
grains, and no matter what solvent, nor at what period of
time, the weight never exceeded 210 grains. I
was able to obtain some other exotic solvents, and did some
brief testing on them. Same results, tad
line: I am almost certain that the problem with
the one-piece float assembly is one of very long term
exposure to a mixture of various solvents in common
gasoline's, and, with the contaminants that such solvents can bring with them....and those gasoline's that have, perhaps,
alcohol and/or MTBE, or similar, might be affected MORE.
The Bing Independent Float 'kit':::
I do NOT recommend Bing so-called
alcohol-proof float kits (dual independent
floats). HOWEVER...if you are willing to fiddle with
these, and understand the limitations, then their use is OK
with me. There are several reasons. Bing said,
years ago, that they would give increased mileage and
performance due to stability of the fuel level during
turns. I agree, but mostly only in an airplane or with serious
racetrack use where the bike is leaned to extreme angles. These independent floats were originally advertised as
being for engines where the carburetors were facing more
left and right than on our Airheads...more or less fore and
aft. One must think about the way the floats
are hinged and operate, and then one will see that Bing's
old claims for our bikes were hardly reality.
As to their NOT being affected by 'alcohol'....that may be
true. For EITHER
the stock OR Independent kits, you MUST replace the float
NEEDLE regularly....as it is the SAME needle, for BOTH.
The Kit float level is somewhat difficult to
initially adjust, having TWO flimsy brass arms. The
arms contact the floats via small pins on the floats, and
if not close to correct alignment, the carburetors can
flood. There is NO provision for an overflow/vent for
the float bowl, as in the stock float bowls, and thus,
theoretically, it is possible for the bike, especially on
the left sidestand, to fill a cylinder with UNcompressable
fuel...which can destroy a piston and rod, ETC. The
overflowing fuel might go on the ground from a further up
carb body port, and not into the cylinder. I would
not count on this. However, the
separate floats seem to be stable for any type of
gasoline's, and MIGHT just last almost forever. There
is an article on this website on the Bing kits....
These kits were
originally sold with plastic bowls. Those bowls have
been known to develop cracks, often microscopic, that cause
weeping of gasoline. The latest Bing bowls are
zinc metal, like the original stock bowls. They are
EXPENSIVE, and NOT available from BMW (BMW carb parts
prices are often MUCH cheaper than Bing's!!).
****NOTE: The old method of
turning the carburetor upside down for adjusting the float
level is no longer used for the STOCK one piece white floats...but it IS for
these Bing dual independent floats! At least per Bing's sheets. However, by using one's finger,
carefully, one can adjust the float bridge of these Bing
kits, whilst on the bike...and Bing's latest sheets reflect
both methods of adjustment.
independent float conversions, here are some adjustment
With carburetor upside down the most outward part of the
brass hinge unit, the top of its flat area, should be 10.5
mm and parallel to the base. AND...BOTH of these arms
MUST be parallel to each other. For the old model 55
carburetors this was 8.5 mm. Once in operation,
one could remove a bowl quickly, and the center area to top
of the fuel should be very close to
1-5/32". NOTE that
after first installing and adjusting one of these Bing
independent float kits, they must be
RE-ADUSTED after maybe a dozen hours of
riding. This is because the float needle breaks in,
and the effect of fuel on the needle and float. Quite frankly, I think the BRASS also tends to change a bit, something to do with its hardness and tempering grade I suppose. It is important that the
spring loaded plunger on the float needle be in good
condition, and the spring inside it not sacked out, or the
mixture will be variable due to changes in the fuel level.
To adjust whilst on
the bike, maintain the arms parallelness to each other, and
adjust for 0.412" from the arm lower edge to the
carburetor body, at the point your finger VERY LIGHTLY
pressing on the arm assembly, causes the float needle
plunger tip to NOT QUITE start moving upwards.
ON the bike, that above adjustment is easier to do by observing
the point gas just stops or just starts flowing....that is the
parallel point, or, should be. The part of the arm to look
at for the parallel-ness is the BOTTOM of the arm.
***There is a complete article on this website about those independent
float kits, well worth your time to read:
in awhile deposits of fuel residues will get into the
needle spring and cause it to malfunction. The float
needle tip also wears out. Thus, the float needle
should be replaced at regular intervals, just like the
stock one, and they ARE the same part....as delivered from
BMW or Bing. I recommend 30,000 miles. It
appears that the floats will NOT require replacing on the
Bing KITS. I'll say it again: The
float needle is the SAME as on the stock carburetors, so it
is available,...from your BMW dealership.
GENERALLY, stock Airhead Bing parts are CHEAPER from the
BMW dealership, than directly from Bing.
Your stock floats are held
into the carburetor by a pin that is knurled on one
end. Pins can wear, although it takes
a VERY LONG time...if yours are worn, replace them. Be
sure to push the pin out in the proper
direction!! A magnifying glass may be needed to see
the knurled end when still assembled. The pin MUST
be pushed OUT with a tiny drift or even a modified nail AT
the NON-knurled end.
When reinstalling that pin, this is not
the time to hamfistedly use ViceGrips or Channel-Locks and
break the float pin bosses. You install the
NON-knurled end first, of course. The floats
be tied to the float needle with an
easy to loose very tiny wire clip. That clip is there
to ensure the float needle releases from the
seat. It is a PIA to install the stock
floats...or the KIT bridge...with that wee tiny wire clip
and the float needle. Just takes practice....see
****That clip is not used on the
The float needle lower end may have a tiny hole in it, that
the wire clip fastens to, and this end part rotates
easily.... some may find it a more than a little bit of an
annoyance reassembling these. When installing the float,
float pin, float needle and that tiny wire clip, they must
be installed as an assembly, a bit tricky, especially if
the carburetor is right side up, but doable. I suggest a
white sheet under the carbs, in case you 'loose' that wire
clip or needle. I highly recommend
that you order SEVERAL of these wire clips when you order
floats and float needles, as they are SO easy to
replace the float needles when replacing the stock
float and vice-versa. When the float needle tip gets bad, the
carburetor will leak
on your foot, the mixture gets very rich, and the mileage
goes way down.
***A very rare problem is a float
needle that seats irregularly, yet a new needle,
sometimes someone even replaces the needle seat, does not
fix the leaking. INSPECT the float tang...it
needs to be flat and NO irregularities in its approximate
center where it contact the bottom of the float needle.
This is very rare since most people have to replace
floats long before this wear is noticeable.
I recommend that the diaphragms be replaced at around
30,000 to 50,000 miles, possibly even 70,000. Some of
this variability has to do with atmosphere (smog, etc.)
and some with time, some with mileage. I have no objection if you let the
diaphragms go until they fail by getting a hole or tear in them.
You usually must remove the slide and diaphragm
assembly and stretch the diaphragm a bit with your fingers,
holding it up to the light, to see holes and tears; but
sometimes they are very obvious without the removal and
stretching. You can
purchase the individual parts if you need or want to. Diaphragms
seem to hold up rather well over time, so I cannot give a
replacement period just for time alone. The type of
components in your gasoline also seem to have some effect
on their longevity.
BMW dealers prices are generally
CHEAPER than Bing prices.....and you can NOT depend on
Bing USA parts being of the same quality as the BMW sold
parts. Be careful! .....and do NOT use
32 mm kits from BMW are 13-11-1-258-051
40 mm kits from BMW are 13-11-1-336-902
The very earliest /5 diaphragms
were replaced by a thicker type, which is all that is
available now. Some of those very early ones might
still be around.
There are a number of rubber O-rings used in the Bing CV carburetors. All should come with the rebuild kit (5 O-rings).
These are BMW part numbers:
13-11-1-257-739 Used at the throttle shaft, 6 mm x 2 mm and rather thickish.
13-11-1-257-819 Used at the enrichener shaft, 5 x 1.5 mm and rather thinnish.
13-11-1-257-812 Used at the main jet assembly, 8 x 1.5 mm.
13-11-1-254-735 Used at both the idle adjustment screw and on the idle jet, 3 x 1.75 mm
The screws for the carburetor top cover are M5 x 12 oval head
Except for the /5 models, lighter carburetor springs are available....they are not the same for 32 and 40 mm carburetors. Check with your dealership; or, Ted Porter's Beemershop in California.
There is a type 606 for the 32 mm carburetors that have 3 digit model numbers; a type 908 for the earlier 2 digit 32 mm types, and a type 312 for the 40 mm carbs.
There have been some problems with the R45, R65, and POSSIBLY some of the larger engines, from 1979 or so, for a year or three after that time. The information from the factory on this problem is sketchy. The problem is poor throttle response of various types, during initial starting and riding off, during quite cold temperatures. Basically, the enrichment device in the carburetors is not rich enough. BMW changed the enrichener disc (that disc with the 'funny' holes) by, essentially, enlarging some. NO change in part number was used. I have the bulletin on it, which, in essence, says to use a new disc, or, modify your disc, by drilling it with specific sized drills, and exactly which/where. I have not posted the SI (are two) on this website, because there are other more likely possibilities for cold starting/running (until the engine has been running a few minutes), such as clogged bowl jet, etc....and, the fact that almost no one rides in such extreme weather, and is not likely to be bothered by a seemingly somewhat slower warm-up period. I can supply the SI.
Do NOT!!!...NOT!!!!...use anything but BMW Dealership or Bing Agency furnished BMW diaphragms!
You may run
across articles that say that you can substitute Zenith
Stromberg diaphragms, used on some Volvo's, ETC., for
certain Bing diaphragms. You also may find
that if you do this, they may work OK, BUT MAY work
marginally. There are differences, in
material/thickness that do NOT seem consistent.
The Stromberg CD150 diaphragm
does physically fit the 32 mm Bing CV; and the CD175 does
physically fit the 40 mm Bing CV. DO NOT USE THESE.
With some Airhead carburetors BMW does
not offer just the diaphragm, and wants you to purchase the
slide with the diaphragm attached. This may
occur with the models where the diaphragm is attached by a
pressed-on nylon ring. If you want to, you can purchase the diaphragm from BINGUSA. You CAN pry the ring off without breaking it ....if you USE VERY HOT
WATER, EVEN BOILING WATER, to soften and expand the ring. Be gentle, do not try to open the ring too far.
I recommend you
do NOT get carburetor rubber parts from BINGUSA; get them
only from a BMW dealership, they will be correct color
and type of rubber, etc. It would be better if you
obtained the diaphragms from BMW dealerships too. BMW dealers prices are generally
CHEAPER than Bing prices.....and you can NOT depend on
Bing USA parts being of the same quality as the BMW sold
parts. Be careful! .....and do NOT use
BMW supplies a screwdriver
71-11-1-103-086 in the on-bike tool
kit. Phillips and standard ends,
reversible. The 'Phillips' end is NOT a PosiDrive nor
is it a Reed & Prince tip.
There are better choices, and stronger, longer lasting, but
it is not always easy
to find a screwdriver that is small, and has both phillips
and slot ends, and fits your tools bag for the on-bike
kit. Some folks purchase one of the SnapOn types,
with assorted hardened magnetic tips that fit inside the
handle. If you have the room and budget, the Snap-On
is a QUALITY tool, that NEVER wears out the tips. Be
sure you have the proper size tips...many come only with a
relatively narrow single blade size tip. The proper
Phillips size is #2.
top " phillips" screws are not always really
Phillips screws, they just look that way at a quick first
could be Phillips, OR could be 'Pozi' type.
Someone might even have changed them to allen head types.
The ancient aircraft tip screwdriver called Reed &
Prince works relatively nicely on the PoziDriv screws....as, of course,
does the real Pozi-Drive. The PoziDriv tip is
EXCELLENT for REMOVING the phillips type, if the Phillips
is way tight. Generally install a real Phillips type
with a Phillips screwdriver, but the other types of screwdrivers DO work
better. If the screws are
frozen, you can try a variety of ideas. The Phillips
type of screw was DESIGNED so the TOOL will SLIP after a
certain torque is reached. This is why removing a
stuck Phillips screw is so annoying. Methods of
adding friction for easier removal includes valve grinding compound for a
better grip. For egregious instances, I use a metal block underneath and an Impakt Driver
with the PROPER TIP. Tips for
interchangeable-tip type tools are available from a
variety of sources, including Snap-On, and the PosiDrive
tip IS available.
Some have installed Allen head screws at the carburetor
tops. They are OK, but don't over-tighten, as many of
these have a very small allen and can round-out more
easily. Some early carburetors had common
slot screws. BMW and Bing may be, and have,
shipped EITHER PosiDrive or Phillips screws......be sure that
your 'screwdriver' fits them.
Remove the screws one at a time, coat the threads...and
under head taper...with antiseize....and
replace the screws without too much torque;.....you will appreciate
these hints much later
red plastic-handled screwdriver that is in the BMW on-bike
tool kit, the one with the reversible insert, probably Heyco Germany brand, is NOT NECESSARILY THE CORRECT TOOL
for the carburetor tops....this tool is a
common Phillips, and not a good one. The PosiDrive screws
generally have some radiating lines to indicate they are
not Phillips type.
Note, again, that the Pozi type screwdriver will usually work well on
Here are photos of the Posi-Drive screw, and the
screwdriver tip. Note the differences from a
Phillips....the nearly flat bottom in the threads and the
corresponding flat top of the screwdriver; note also the
angles and the extra (lesser) 'splines' in-between the
Diaphragms may have a downward facing tab that fits into a
small recess in the slide itself. Diaphragms have a
somewhat larger downward facing tab that fits in a
corresponding slot in the top of the main carburetor body.
Tabs and slots must
line up during the actual fitting of the parts, and it is
easy to accidentally rotate the diaphragm when putting the
carburetor top back on. When assembling the diaphragms to
the slides, be careful that you assemble things
concentrically and carefully. If the needles are still in
place, be extra careful
not to bend them!!! Tighten the top of the
carburetor screws evenly, coat the threads and underside
with a WEE tab of antiseize, and do NOT overtighten..
With the central jets parts
assembled, some care and wiggling may be necessary to
install the slide and needle assembly in order to get the
needle into the lower brass tube area. NOTE that many
have initially assembled the atomizer jet wrongly. In the
Bing CV carb, that atomizer must
stick UP INTO THE
CARBURETOR THROAT. If you assemble wrongly and then
put a wrench and some force onto the central jet
assembly, you can destroy your carburetor.
The central jet assembly top-most
piece is a tubular brass part with some holes (this item
is called an atomizer). This loose part (as you
begin reassembly) fits directly above the tubular
part called the needle. This atomizer must
stick up INTO
the carburetor throat, and only
ONE end of it has the correct
diameter to allow it to fit up
into the throat. A problem can come about
if one has the slide, diaphragm, and its wiggly needle already in place in the carburetor, and you now try
to install the central jet assembly. First, be sure
that the black rubber O-ring on the central jet assembly is
in good condition,... if questionable, replace it, and use
a wee bit of silicon grease to help its installation, AND
on the outside of the O-ring (I also place a WEE bit on the
threads of the jet assembly) so the jet screws upwards
easier. Regarding the mentioned potential problem: When
installing the atomizer, ETC....be VERY careful that that
the proper end fits into the throat, and that the needle
does not catch the edge of the jet....you might not notice,
and then screw the jet upwards, bending the needle...or
worse yet, applying too much force and breaking the
threaded carburetor boss. NO excessive force is
needed here!!! SO, if the
slide with its needle is already in the carburetor, be
especially careful installing the central jet assembly.
reinstalled into the carburetor clean and dry, and
the lower jet assemblies that the slide needle fits down
into, really should, ideally, ALREADY
be in the carburetor!! If you are careful, see above
paragraphs, you will be OK.
When assembled correctly,
the slide, which has two holes at the bottom, off center,
will have those two holes facing the cylinder
head. Slides work OK even when fairly well
worn. Bing has been offering some slides
with O-rings. They are quieter, in a few instances of
Since wrongly assembling and using force with the slide,
needle, and central jet, can damage the carburetor parts
badly, I will get into this a second time, a bit
When you install the main jet, and the parts associated
directly above it, it is best NOT
to install these parts after, BUT
BEFORE you install the slide/needle/diaphragm
assembly. Failure to follow this advice can lead to bending
the slide needle, you can cause a real hang-up inside, which
is hidden from view, and further tightening of the jet
assembly using a 10mm wrench can cause you to, in the worst
case, split the carburetor boss. This is nasty to fix, most
folks just replace the carburetor, or, the body of it. Some
do an epoxy job, which MAY
or MAY NOT work.
Sometimes a sleeve is made and installed, perhaps epoxied
also. A new carburetor body is REALLY
expensive ...unless you find a cheap wrecked
bike to remove it from. Old hands at working
with Bing CV carbs install any way they want to, as they
know the feel, do it with fingers initially, and also
have their other
hand's finger moving the slide needle at the same time,
typically lifting the slide fully up. This WILL work
well...and is OK for you to do, just be gentle and watch
what you are doing.
Sometimes the brass atomizer part
that sticks upwards into the carburetor throat does not
fall downwards and out when the central jet assembly is
removed, or does it later when you are not looking!
Use a toothpick or similar to gently dislodge
it. It is easy to lose these parts, so do
NOT! Remember, I recommended an old piece of
white sheet under the carburetor if on the bike. Once in
awhile, that brass atomizer part does not seem to want to
go into position...it is usually just a wee bit of crud on
it or in the carburetor body hole. Insert the
atomizer as squarely as you can after cleaning the hole and
atomizer, and it will install OK. Remember that ONE
end is slightly smaller than the other, and only that end
When one does a mini
field-overhaul on a Bing CV carburetor, it is usually not
necessary to totally disassemble the carburetor, removing
every jet, every O-ring, the enrichener parts, etc.
Normally, one really needs only to replace the diaphragm,
float, and float needle and spray the passageways a few
times with a good cleaner. If you removed the
idle mixture screw, replace its O-ring, slightly coating it
with silicone grease. At some goodly mileage
(Bing says 25K, I say 60K), one should replace the slide
needle and needle jet. The reason to replace these is
that the needle is designed to vibrate freely, and the two
wear each other and change size, the result of which is a
richer midrange. Yes, cheapskates can lower the slide
needle one notch to sort-of compensate, but even with very
high mileage, this is usually way too
much. Some late model slide needles
were aluminum...and the GROOVE wears very fast....they are
to be replaced as soon as this is noticed.
HINT: When installing O-rings, put some common
electrical tape over the sharp threads, and use a tiny
amount of silicon grease to ease the O-ring into its
groove. Remove the tape afterwards.
One should remove only the necessary
parts, then spray into all the jets (pilot jet, mixture
adjustment hole, bowl jet, central main jet assembly),
etc., with a strong
carburetor spray, and let sit awhile, then spray again in
every direction possible through those holes. I prefer Berryman B-12,
in a version
called 'Carburetor and Choke Cleaner' for this job.
This is a very strong solvent mixture that actually
dissolves most all of the deposits from gasoline, which
many other spray solvents do not! You might
consider spraying all the metal pieces, then flush with a
common spray brake cleaner or equivalent. I do
recommend removing the central jet assembly, it tends to
get cruded up, often with 'black' stuff. Be careful,
as has been cautioned above, when replacing.
Removing the idle mixture screw and spraying
all the idle passageways with that very strong Berryman
product is a good idea. Spray three times, waiting a
bit each time. Use plain clear silicone grease, or
Dielectric Grease, from your autoparts store... LIGHTLY
on anything brass that screws into anything (antiseize is
OK), and silicone grease for any rubber O-ring.
Use of silicone grease will tend to protect the O-rings
from being damaged when installed, as well as greatly
lengthening their life, and making things turn
keep in mind that there are some VERY SMALL holes in
certain passageways and jets, and you do NOT want grease
Some Bing carburetors, such as the
R60/6 and R60/7, use an acceleration
jet assembly in the central assembly, these parts all come
out mostly at one time, same as those carburetors
Some carburetors have the diaphragm held in differently. Be
careful expanding any plastic rings/clips, they can crack.
A tad of heat from a
hair dryer, on the plastic retainer, or in very hot water,
NEVER clean jets with tiny drills, etc. There is a
danger here that you might increase its size.
It is probably OK to clear a jet with a very thin wire, but
be careful. Typically a wire is not needed, if spray
solvent is left in place a few moments, and then
ENRICHENERS...yes, a whole choking section on this subject:
Introduction: This section, 'enricheners' may seem quite complicated at first, it is not, really.
If you take a carburetor apart, you need to be able to assemble it in the correct positioning
of the parts. That is usually actually very simple. HOWEVER, some carburetors were MISMARKED
by the Bing factory. ALL will be explained in this section. Read it through, then repeat, and
LOOK at YOUR carburetor parts.
A cleaning and
VERY LIGHT silicone spray or silicone grease lubing will
make its operation smoother. If the rotating
disc, which has holes for jetting, gets plugged (unusual
unless you use grease),
the enrichener won't work correctly.
pieces are easy to mix
up and get installed backwards...or get the left and
right carburetor enrichener parts mixed up. A good rule is to
do both left and right carburetors at the same time. Your
bike could ALREADY have them assembled wrongly.
The enricheners be assembled correctly for
the 'choke' to operate correctly; AND...in the FLOAT BOWL,
the corner jet in the well must be clean and UNclogged.
There are two very tiny pipes that must be good, and UNSPLIT, one comes down into the enrichener well of the bowl, the other is in the middle of the bowl, and vents to the underside of the bowl. Once in awhile water collects in the bowl, freezes, and these teeny pipes split.
enrichener parts orientation....
The left side photo, below, shows a dot-dimple on the
enrichener shaft, which, if correctly marked and
installed, points to the cable-fastening end of the
lever. Later model carburetors have two slightly different levers plates,
with a notched slot for the cable, & hole for the cable
barrel. I have a photo of them a bit further down.
It is possible that some shafts have the DIMPLE, as in the left photo, REVERSED
by mistake, during assembly of the disc/shaft.
This can happen for the right or the left carburetor. By using the views of the inside of the assembly, you can be sure your carburetors are correctly assembled, even if mis-marked by the Bing factory.
NOTE!...it is possible for the
SHAFT to be wrongly inserted into the disc. The disc on the shaft is spring loaded. This is
particularly so on
the models with the disc type, that, pressured lightly with your
fingers, moves on the shaft. Remove the nut, which will
allow the choke lever(s) parts to be removed, noting how
the lever parts were attached. If you assemble them
wrongly, the cable barrel will not fit correctly!!!
See a bit further down the page for a more detailed
Below two photos: one on RIGHT has shaft market R
this is from a 1978 Airhead RIGHT carburetor.
Early carburetors have the number of tiny jet holes
and the elliptical-tail slot different, with some
holes missing. There are at least two styles of those.
Although it would be nice to have the dimple, see the
left photo below, such that it
really does point to
cable barrel as designed, it really
makes no difference,
long as the cover with its parts
fits the carburetor in
That position, for the RIGHT-SIDE
carburetor, is shown in the
right photo of the two photos below.
If you are more
curious, NOTE where the elliptical hole, and
also the small
jet holes align to the body of the carburetor,
start to place this enrichener cover/disc/shaft assembly
the carburetor. There are body passageways they
with....but you might get confused, trying to figure it
The lever shown in the left photo is the ONE-PIECE
used on the very early carburetors.
If you were to look at a LEFT carburetor disc and shaft (instead
of the RIGHT, as below), you would see the tail of the
hole pointing the other direction.
NOTE...the right photo should NOT be construed to have
shaft/lever in the position of the left photo.
Photos of the enrichener with the lever in the two
extremes of positioning are a bit below.
The brass shafts that
operate the enrichener are stamped in the inner ends, L and
R for Left and Right carburetors. The stampings can
be a bit vague, see above right photo. The late models (well after early
/5 CV carburetors) rotating thick metal disc has an
elliptical hole, and 4 smaller holes, one of those 4 is a
bit bigger. The holes MUST be clean/clear! There are
numerous types of the discs, some will not be machined
with the elliptical hole through the disc...and different
holes sizes and arrangements may be seen.
Besides the photos, above, and below, here is a TEXT explanation,
for both left and right carburetors:
If you were to have
the LEFT carburetor enrichener unit off the carburetor, and
put it in front of you, upside down...that is...you are
facing the inner (disc) side...and oriented so the round
protuberance of the outer casting is TO YOUR RIGHT, and the
LEVER is UPwards to its stop...about 1:00; THEN, the elliptical hole of the disc is roughly
opposite the upper left casting screw hole, say
11:00....and the 4 tiny disc holes are roughly to the lower
For the RIGHT
carburetor enrichener unit, as in these various photos, for the SAME orientation of
casting and lever...the disc is REVERSED...that is...the 4
holes are to the UPPER LEFT, and the elliptical hole is to
the lower right.
Here are some photos that will
further explain things:
The above photo, marked
WRONG!! has the dimple in the wrong
direction. This MAY be necessary if your DISC/shaft
is wrongly assembled or wrongly stamped!.....by the factory!
PLEASE RE-READ THOSE TWO SENTENCES AGAIN!!
Later model Bing
CV carburetors have two-piece cable levers. It is possible to WRONGLY install the two metal pieces. It is annoyingly
EASY to overlook this, and you won't notice until you have
the carburetor fastened to the engine. Lever parts can be installed upside down AND/OR reversed in
position. In BOTH Left and Right carburetors,
the part that has NO notch (no slot)
for the installation of the cable wire, goes onto the carburetor enrichener shaft first, with its offset facing the
carburetor body. The outer part, that DOES
have that notch (slot),
can be installed wrongly, flipped-over if you will.
Install it such that the notch does NOT
face upwards during cable operation.
Here is a photo of how the later
model levers look when
installed properly; not a great photo, but you CAN see
the SLOT in the top part for the inner cable. The shaft nut and waverly locking washer are not in this photo.
This levers arrangement applies to both the enrichener and the throttle.
NOTE that for a
smooth AND PROPER enrichener operation, the enrichener needs to be
faintly lubricated, cables good, and operating lever cable
lubricated (IMPORTANT or cable can break strands!)... and if you have them, the T barrels under the
fuel-tank where the one cable from bars splits into two, in good
condition. There is an O-ring internally on
later enrichener models. I lightly silicone-grease that O-ring.
NOTE that the fuel bowl gasket MUST BE IN GOOD CONDITION for the PROPER operation of the enrichener. The reason for this is complex, but a simple explanation concerns the tiny diameter pipe that comes down from the enrichener circuit in the carburetor top body, and dips into the enrichener fuel well in the bowl. That tiny pipe has one or two holes in it ABOVE the pipe lower open-end. Vacuum, during the starting sequence with enrichener (CHOKE as marked on the bars assembly) ON, causes fuel to rise in the enrichener well in the bowl to a higher level than in the rest of the bowl, creating even more richness than might otherwise be possible. If the gasket is leaking air, the maximum enrichment will be LESS.
Note too, that due to the over-all enrichener design, the amount of enrichener to be used, and whether or not you need a bit of throttle opening during cranking/starting, and after just starting, can be rather variable.
Most owners booklets say to not open the throttle, as it defeats the enrichener, and this is really a vast simplification and not really all that true. You very well MAY need some throttle opening during starting, and this depends a lot on the particular motorcycle tuning and temperature, fuel volatility, etc.
In cool or cold
weather, full choke may be
needed for starting AND,
very contrary to all the 'books' nice verbiage, you MAY
NEED to manipulate the throttle during cranking.
In one version of Clymer's manual that I saw, in the early
section on how to start your motorcycle, Clymer's has the
operation of the choke lever (on the early models where
said lever is on the clamshell of the air cleaner housing),
BACKWARDS. The truth is that the
lever must be HORIZONTAL for the choke to be OFF....and
DOWN for choke ON.
Very early Bing CV carburetors have pressed-in float bowl enrichener
jets, not screwed-in.
The enrichener (choke) is held to the
carburetor body by 4 screws. These
screws are infamous for loosening. If the
carburetor is still on the motorcycle, I recommend, that
once the throttle and choke cables are removed from the top
of the carburetors, that you loosen the carburetor adaptor
clamps and rotate the carburetor to allow the tightness of
these 4 enrichener screws to be checked. If loose,
either tighten; or, remove and use a wee drop of Loctite blue
and then tighten them. They CAN be tightened without
rotating the carburetor, but it is typically a big hassle, even
with several types of offset screwdrivers. If you take the
enrichener screws out, clean them and their holes, and use
a small amount of blue
Loctite on the threads before
tightening. BE SURE
that the gasket is OK....the gasket tends to get sucked in, or otherwise
distorted, if the assembly gets a bit loose. I
recommend the faintest possible smear of some sort of
NON-silicone gasket sealer on both sides of the gasket
and the metal surfaces. REALLY faint!
Gasgacinch; Permatex Form-a-gasket (non-hardening), etc.
NO RTV HERE. The reason is not to
prevent leaks directly, but to prevent the gasket from
sucking-inwards, which then DOES cause leaks.
IF you are worried
about using too much silicone grease on the enrichener disc, use silicone oil
spray on the enrichener innards. When I use silicone
grease on the disc I use it very faintly wiped with my
fingertip to a very thin layer.
***Do not think
about removing the throttle butterfly valves unless the
shafts are really worn or leaking, as they are O-ring
sealed, the screws peened, and the shafts can still be
leakproof with a fair amount of side play due to the
presence of the
O-rings. To test for leaking, spray the shaft area from the
outside of the carburetor, where the throttle lever
attaches, with brake cleaner, while engine is
idling. The idle speed must not change.
If you do change the shaft O-rings, DO coat them, a bit
more heavily than faintly, with silicone grease. They
will then last almost forever, and operate
smoothly. If you DIP the carburetor into a
cleaning tank for any period of time with the usual harsh
carburetor chemicals as used by professionals, you will HAVE
TO replace the shaft O-rings. If the shaft is removed, then you must decide on the
screws, to replace or not, to peen or Loctite.
butterfly can be put in backwards. Do
NOT!!!! That is why I previously said to mark
the butterfly!..top, rear...or similar. This is a
The fitment of
the lower edge (and the sharp shape at that point) of the
butterfly is critical where it comes close
to the the idle passageways holes at the carburetor
bottom. Putting the butterfly in backwards will
eliminate any chance of proper off-idle throttle
performance. This is doubly
important with a dual plugged machine in which the
butterfly is more closed at idle. If you
install a butterfly wrong, you will NEVER have a good
stable idle. When installing the butterflies... as you slowly tighten the two
screws, you must lightly
press the butterfly with a finger, into the main carburetor bore,
to align the butterfly...it is important that it fits the
bore very evenly, and for minimal clearance (shine a light
through the carburetor as you look from the other side).
The later enrichener (choke) control and all throttle
controls on all the carburetors, each have an outside return spring.
The springs are not the same. The old style
carburetors had the enrichener (choke) lever on the aircleaner
housing, and springs were not needed as the cable inners
were very stiff single strand of steel wire. The
lever assembly at the snail housing can be disassembled
and cleaned and lubed, as they tend to get stiff with
age. It may be necessary to adjust a size of a thin shim to allow smooth
action...as you do not want the nut loose. Sometimes
that area takes some fiddling with.
styles of throttle return springs were
used. The earliest type fit AROUND the throttle cable
center. It was not a good type, and the throttle was
pretty stiff. Later types had the springs
attached to the throttle lever and a carburetor boss projection with a
tiny hole. If a spring is stretched or
misshapen, replace it. On the
old style carburetors, that stiff spring must not rub
against the carburetor, if it does, change the inner
fit to outer, where the cable barrel
joins the lever. Far nicer throttle feel
can be had by modifying the oldest style CV carburetors so
that the spring is NOT wrapped around the throttle cable
outer sheath. Not a simple thing.
Hate to repeat myself, but....If
you remove any jets, etc., that have O-rings, you SHOULD
replace those O-rings. I prefer to put a faint
smear of silicon (or even petroleum) grease on
the O-rings when assembling to help avoid cutting them
(the tape over threads helps as does room temperature or
a bit above, as opposed to freezing weather). Also
I put a faint amount of silicone grease on the threads
The one jet ASSEMBLY that I always recommend be removed, to
clean that area in the carburetor is, in order from the
bottom (for your future reference): the central main
jet; the washer above that (do not substitute the type of
washer, don't leave it out); the so-called mixing tube
(brass part, with O-ring and outside threads, with 10mm hex
sides) above that; the needle jet above that; and the
atomizer above that. This information is for those who have
removed things, have not 'seen' the direction of assembly,
or have forgotten the direction of the parts. If your
carburetor has the acceleration pump assembly, it is slightly
different looking. Note previous cautions about
screwing in the central jet, not to trap and crush the
needle, and note also that the
atomizer (the top most part) fits only one way, and it will
then, properly, stick upwards INTO the throat.
The needle jet, which looks like a
machined brass tube of two basic diameters, and is often
marked with a number, such as 2.64, 2.66 or 2.68, fits with
the small tube portion upwards and its slightly curved
[internally] end downwards. Above that part is the
atomizer, which is a machined brass part of three differing
diameters, the slightly
smaller diameter goes upwards and fits through AND
INTO, the carburetor venturi (throat), and its
lower portion has the holes. On RARE
occasions this part might not seem to fit and does not seem
to want to poke up through the carburetor into the venturi.
If the smaller diameter end is up, the side-holed end down,
this is correct, and you may have the part slightly tilted,
or, tilted and under a tad of too
much pressure from the 10mm wrench area below. You
can install that atomizer by itself, and hold it IN the
throat, perhaps using a toothpick to get it properly into
position and then fingers to hold it in the throat, as
you assemble the lower parts.
You MUST assemble the
central jet assembly parts in the correct order. Do
not over-tighten. If the slide/needle is
already installed in the top of the carburetor, be
cautious about not letting the needle hang up on the
central jet parts!
The central jet assembly O-ring, with
the faint smear of grease, will reduce friction, and you
should be relatively gentle on the force you use on the
10mm wrench, just barely tight. Antiseize or silicone
grease on the brass threads make for less
corrosion and seizing possibilities. Remember that
the carburetor body is made of a soft and not overly strong
material....zinc probably. The danger is in cracking that
central carburetor boss. I grease the threads
lightly, silicone or anti-seize. Those
that over-tighten the central jet assembly, and fail to use
a lubricant or anti-seize, are asking for seizure, years
Cleaning the idle system...jet, holes, etc...is important,
and the Berryman's works well, if allowed to work awhile.
DON'T bugger the end of
the idle jet with a poorly fitting screwdriver.
Rarely the idle jet has been known to freeze
in its threads. If you break off half of the
screwdriver slot end, drill it carefully and use something
like an EZ-out. I will use heat on the
surrounding alloy, to try to enable removing, before going
replacing rubber O-rings which you must push over threads,
you might have the thought that the threads might cut the O-ring...yes, they
could. A simple way of avoiding that
possibility is to not only grease the parts with a very
THIN layer of silicon grease....but to wrap a single layer
of any sort of tape around the threaded part, and THEN
slide the O-ring over it!
Don't fail to spray clean the jet in the 'well' of the
bowl, and the overflow tube too. I've sometimes had to poke
around at that jet with a piece of wire to clean it.
The left and right carburetor bowls are NOT the
same. The corner well, containing the jet at
the bottom fits the tiny diameter tube projecting downward
from the carburetor body. This is the
I always clean the various metal
parts with the mentioned Berryman's brand of
carburetor/choke cleaner spray. For a major overhaul,
take everything apart and use a professional cleaning
tank if you have one
available. There are many types of spray
cleaners available at your local auto parts store. Some are
NOT very good. A good one will instantly dissolve a fair
portion of the brown stain deposits if you have some, on
the carburetor outsides, sometimes a cotton
swab will help. I prefer the spray by Berryman, called B-12
Chemtool, Carburetor & Choke Cleaner. This is
nasty stuff. Hopefully Government regulations will
allow it to continue to have the strong formula. Use outdoors, or with your garage door
open! It is also very good in just spraying off the
stains on the carburetor outsides now and then.
Common so-called 'brake cleaners' are AWFULLY BAD at
cleaning carburetors properly.
Be sure the main jets and needle jets have the proper and
same size number on them, left and right. If you have
removed the idle pilot jet, be sure the numbers
Every once in awhile, someone asks about removing, or
changing the setting of the slide needles. Even when
there is a definite reason, such as gross modifications to
the exhaust system, or the carbs are U.S. specification and
you want to richen to the British specification by moving
the needle position; changing the needle position by one
notch is often WAY too much, and the better method is to
change the needle jet to the next size. In
many instances the British-shipped carburetors have both
needle size and needle jet size BOTH changed. This is
almost always the better approach. Another approach
is to ASK BING!...they are usually quite helpful...and
their carburetor parts and service booklet is worth the $.
installing or removing a slide needle, the most common type
of needle is the twist/push-pull/turn type. For them, the
proper method is to clean them and your fingers, so they
both are clean and dry, and grip the needle tightly with
thumb and forefinger, and rotate left or right, pulling
slightly downwards or pushing upwards. EACH 90 degree rotation will allow
ONE needle notch of change (if also pushing or pulling).
UNDER NO CIRCUMSTANCES BEND THE
NEEDLE. Rotate one direction, then the
other, as required. Some may find that a thin piece of
leather will help. NEVER use
pliers!!! ONE (1) 90
degree rotation per so-called needle position!
Be sure both carburetors have the
needle sticking out of the slide the same amount. Use
a caliper, and measure closely. ***I
HIGHLY recommend that you check the
slides/needles for distance, to be sure they are the same,
as well as to write down the distance, BEFORE
removing or installing or changing the needle position. You
cannot 'see' the needle position, it is done by feel, and
having a measurement (you need to be accurate to maybe +-
.015") may save you some considerable hassles. I
measure them with a common vernier caliper. You can
measure the underside of slide-to-tip distance, or, the
distance from top of slide assembly 'tube' to needle tip.
Needle position (there are typically 4 positions available)
is measured from the top slot position of the needle. Most
needles are in the #2 or #3 position from the top.
other, later type of needle is not held in by the hidden
clip in the same manner. There is a screw in the top of the slide. Remove the
central flat-head screw from inside the slide, and
turn the slide over. The needle should fall out the top
into your hand, with a little clip on it around one of four
SLIDE needles should be replaced at the 60,000 mile
intervals I recommend, or tad sooner, with
the associated needle jet.
is a particular problem with the aluminum or similar needle material on some
1985+ models, in 32 mm size. There may be some
other carburetors with this problem. The NEEDLE
grooves WEAR, due to the type of metal
used. If the groove wears enough, the needle
will not deliver the properly metered fuel.
Watch for this, it is little known. Replace the
needle and the clip! You can get weird
symptoms, even backfiring, if things wear enough.
Check BOTH carbs!...they do not, for whatever
reason, wear at the same rate.
The carburetors should be mounted
squarely to the motorcycle. View from the top, and a few
feet to the rear of the bike. Do NOT tilt the tops
towards, or away, from the motorcycle.
The rubber 'hose' adaptors from the carburetor to the
cylinder heads are sometimes found to be leaking.
This is usually proven by spraying them with any spray
cleaner such as 'brake cleaner' at idle speed...should be
no idle speed change. Keep the screws on the band-clamps
tight. This is the perfect time to spray the
throttle shafts too. NO
idle speed change at all is proper and acceptable.
CARB TOP STAINS:
Fairly often I see carburetor top stains where they join
the body of the carburetor. The tell-tale sign is a brown
(usually) stain around the diaphragm joint interface,
caused by some tiny gasoline weepage. I was never
bothered by this, as the 'problem' is sporadic and
minuscule. However, Oak
sent me (in 1984!!) a bulletin he made up describing this
situation as not necessarily being caused by the lack of
the diaphragm acting as a seal, but rather that the
compression of that diaphragm was insufficient for a
COMPLETE sealing. He recommended removing the carburetor
and flat sanding the carburetor top itself, with 220 grit wet type paper,
kept wet with water,
figure eights, carefully, until the groove, which he said
was 0.155 to 0.156 inch deep in the troublesome carbs, is
reduced by about .007 inch. He said to shoot for a final
depth of about 0.147 to 0.150. Remove all grit. I have done
this to several carburetors, and it DOES stop the staining.
Frankly, few of you have the gauges to measure this, so you
could try just a few
figure eights. TEN is appropriate, medium pressure. Do them EVENLY,
with even LIGHT pressure. Once the fresh sanded surfaces
are evenly fresh all the way around, that is likely
enough. Do not overdo this. Clean and reassemble.
LEAKY TOP PLUGS:
Some carburetors (not the flat top ones) have had leaky
steel plugs on the domes...that shiny center area. You can
easily test the plugs for leaks when the domes are off for
servicing the carburetors. DO NOT
allow any leaks...it will act like a torn diaphragm. They
can be crimped or epoxied. I prefer crimping with a tiny
tip punch and then epoxying. Some folks have used a
toothpick and aluminum paint. If your plug has
a letter C stamped into it, do not cover it up, it means
something....it identifies an early modification in the /5
era. There is a BMW Roundel that can be
epoxied to the top of the carburetors (they fit the small top ones, also the flat top ones, which can also use much larger ones too).
article on this website, for a huge list of Roundels,
including exactly which fit nicely the small tops.
When cleaning the area for epoxy or aluminum paint, etc.,
it is very difficult to get sandpaper into the corner.
I use a dental pick or awl.
HARD STARTING, maybe ONE carb
does not work well initially, then works OK after engine running
& throttle opened:
If starting is still poor, it may be that the slides are not returning
fully. Older advice was to check for that and
fix by installing springs 13-11-1-335-324 above the slides
on 40 mm carbs, and 13-11-1-338-134 on 32 mm carbs. This did not apply to the flat top carbs.
Tom Cutter once said that this modification, installing a longer and softer
spring on the slide, will smooth the idle transition at the 1/8th
to 1/2 throttle movement. Tom said that the shorter,
earlier spring, used on the 40 mm Bing CV carbs, was
13-11-1-335-324. He installs the longer softer
spring 13-11-1-338-134, as used on the 1988-1995 R100 models
using the 32 mm carbs (these springs, per Tom, are used on the
EURO R100GS 40 mm carbs).
I have my own input on this, besides the earlier paragraph. Some
folks DO prefer the more abrupt throttle action of the stiffer spring, which is
about 115 mm long and has about 30 coils. The softer springs are about 120
mm long and have about 20 coils.
If you have done most everything, and
you have problems starting the bike, consistently hard
starting, or maybe ONE carburetor is acting up, that
cylinder not firing (maybe even until engine warms a bit)
and throttle is opened.....check that the enrichener was
properly installed, no matter if the dot-dimple on the shaft looks
correct.....and if still a problem.... see if the butterflies were properly
installed. Not only is this to include loosening the screw whose bracket
keeps the shaft in place, but loosening the butterfly screws (a problem if peened, if not, when tightening, use Loctite BLUE), and be sure the butterfly
will completely seal to the carb bottom.....and tighten things
again. If the butterflies are reversed, you will never get proper
If you have a R75/5 that is particularly a bear to start (or,
one carb is not working at startup), and everything else checks out fine, be
SURE to check the slides, to be SURE they are BOTTOMING fully, and not
hung up slightly. Install the springs above the slides.
This problem is rare, but has been seen on them, and VERY rarely on
later carbs. Polishing the slides and inside carb body can help.
There is a very complete article on this website about
the R75/5 carburetor problems: http://bmwmotorcycletech.info/earlybingR75CV.htm
there are complaints of hard-starting bikes. The owners
have checked everything, including valve adjustments, compression
pressure, spark plug wires and caps, coils, everything....and the
bike still does not start OK. Check the slides on CV
carburetors, be sure they are fully bottoming.....there is a
spring on top of the slides on some models, to help with this.
ON all models, and the Independent float KITS too;....the
floats are adjusted by bending the tab
that the float needle (and wire clip, if used) attach to. I
have found a TINY screwdriver does this OK, and seems to
work better than unwieldy long nose pliers. Do one
carburetor at a time. BE GENTLE
AND CAREFUL!!...do it evenly too...not just at one
edge, which bends the tang on an angle you don't want.
In other words, keep the tang flat and square.
After making a small change...
turn gas on, lift float gently and SLOWLY with
protectively gloved finger, until the gas flow JUST
stops. At THAT point where the gasoline JUST
stops flowing, the top of the stock floats are to be
parallel to the lower body of the carburetor. I allow as
much as .020 inch below, maximum. I have done some
fine-tuning by playing with the float level, I suggest you
do NOT. Some
folks find it easier to lift the float until the gas stops
flowing, and then very very gently lower it until the gas
JUST flows. This MAY well be
the preferred method, as it eliminates the effect of the
spring loaded lower tip on the float needle and eliminates
any play in the pin and hinge holding the floats in the
For the KITS, the adjustment is the same, but the measured
distance is .412" from either lower arm edge to the
I have information on this website
....originals of some Bing documents, some of marked-up copies, crude, but useable...all of various Bings sheets on
installation and adjustments of the independent floats KITS. Here is a
Be gentle and careful about doing any
bending. Float level affects richness-leanness and gas
Major tuning/adjusting the carburetors is not part of this
NOTE and HINT: The band clamp at the carburetor throat inlet USUALLY should have its adjustment at the TOP...or, at least not at the bottom. The curved intake plastic tube fits in
most models only in one direction. If fitted
wrongly, things do not line up well. If the
band adjustment is not above the bottom, the breather
output oil may drip on your foot, depending on if there is
a slit or not on the tube; this was particularly so on the
earliest models. The intake plastic tube
can be slotted for easier use.
Additional information on Bing CV
carburetors will be found at http://bmwmotorcycletech.info/bingcv-2.htm
to 12-07-2002: mostly
Through 12-09-2002: add area for upcoming float
testing; added references to Bing CV Carburetors-2,
clarifications and emphasis items. This
version was not to be released to
the website, pending more
01-30-2003: Updated many places, decided to release
to the website even though float testing has not
begun yet. Added a complete section on
the enrichener orientations.
03-30-2003: extensive information on Bing dual
independent floats added.
06-21-2003: Add NOTE and HINT on band clamps.
07-13-2003: Add all information on float testing
done; clarify many areas.
07-14-2003: Edit for clarity
07-20-2003: Add note on float/float pin clips not
being used on some models
07-22-2003: Expand about the two types of retaining
for the slide needles
09-30-2003: add top of article notes on Gary L.
09-30-2004: add url for Bing's chart of component
description and numbers
02-15-2005: minor updates.
02-18-2005: hyperlink to bingindependent.htm
11/30/2005: update enrichener/choke information
04/23/2006: add emphasis note on screwdrivers for the
Bing tops. 04/24, modify that again
05/11/2006: Bing diaphragm caution note
08/24/2006: Add photos of enrichener
parts/orientation (left parts)
03/04/2007: more information on the Stromberg
diaphragms and cautions on their use.
05/03/2007: Fix hyperlink to BMWMOA.org; and
generally update the entire article
07/06/2008: replace enrichener photos with better ones.
04/19/2010: Expand description of the enrichener
parts assembly and alignment, regarding the dimple,
later in evening, add more comments, so is no mistake
about how the
enricheners all assemble.
04/25/2010: Add photos, Posi-Drive screws and
today go through the entire
article, simplifying, changing to more legible & less
fonts & colors. Especially, fix the Enrichener
section, making clarifications,
adding photos, etc.
Final version release 3:12 PM PCST
02/16/2011: Added another view of enrichener cap
Clarify the enrichener a tad more, and remove one photo
that was confusing.
08/15/2011: Revise diaphragm and Stromberg
05/14/2012: add butterfly photos
05/17/2012: Clarify information on the slide springs.
10/14/2012: QR code and google update code
11/06/2012: Expand Bing independent
10/09/2013: Add more to information on float needle and seat.
07/15/2015: Update a few areas for increased understanding/clarity.
copyright, 2014, R. Fleischer