Fuel system in your Airhead BMW Motorcycle---
Tank cleaning methods; premium vs. regular; fuel additives;
fitting other tanks, seats & fit with various tanks;
throttle & choke cables; fuel hose;
Tank sealants & liners;
©Copyright, 2014, R. Fleischer
>>>Refer to article #1A, #1B, & #75 for more information<<<
>>>An article that describes Lead Substitutes, in depth: >>>
1. An extensive article on Dell'Orto's, covering all their carburetors:
It explains in great detail not just how the Dell'Orto works, but is applicable in general to all carburetors....&
MIGHT be worthwhile for you to peruse, even if you don't have one of these carburetors, which was used
only on the R90S Airheads.
2. If you have a high compression ratio airhead (modified later type; or, 1979 & earlier type with stock
medium-high compression ratio), & you use high octane fuel, be advised that when fueling up at a service
station, it is VASTLY better NOT to fuel up at the type of 'pump' that has only ONE nozzle/hose. Your fuel
may be diluted by a modest quantity of lower octane fuel remaining from the last user...from the internal
valve, pump, etc....through the hose, etc....somewhat depending on the type of equipment in use. The
dispensing companies don't offer this information easily, & 1/4 gallon or more is VERY common.
There is an old controversy over possible increases in combustion chamber temperatures, ETC.,
when using premium gasoline's in lower compression BMW airhead engines, where lower
octane is supposedly not needed. Gasoline burns at about the same rate under normal, that is
not detonating, etc., conditions. The output (BTU) per gallon of Premium gasoline is potentially
....or even likely...to be a small amount LOWER than for Regular. THE ENERGY CONTENT OF
FUEL ALSO VARIES WITH THE SEASONAL CHANGES OF THE FUEL! I think it is likely that
SOME premium gasoline's WILL give LOWER gas mileage than a regular gasoline will.....
assuming the engine ran properly on Regular grade gasoline. Winter gasoline blends tend
to have rather volatile things like butane or propane in them to make it easier for engines to
start. In the USA so-called oxygenates, such as alcohol, are added to most fuels. These
additions GENERALLY cause 6%-10% POORER gas mileage. They are NOT good for your
engine, carburetors, hoses, etc. All the oxygenates tend to cause the engine to run leaner.
Some Airheads are already running on the lean side of best power mixture...& more leaning will
cause stumbling, etc.
3. There are a number of types of aftermarket fuel filters on the market, metal ones, cleanable element
ones, various sizes, colors, etc. I prefer the impregnated paper type, NAPA #7-02323. That number
may have to be entered at the store or on-line as 702323. With the aging of our fuel tanks, even with the
in-tank or in-petcock screen filters, I feel that a decent aftermarket filter is a must, in the line just below the
petcock. There is a much more complete article on this website on the fuel filters, petcocks, etc:
NOTE that due to the age of our airheads, I am a firm believer in using aftermarket paper filters BELOW
the petcocks, & maintaining clean petcock mesh screens. Tank debris is a prime cause for a gasoline
soaked foot (besides old worn float needles). The 'stuff' gets right by the tank mesh screens....which are
designed to trap bigger particles. I clean the petcocks thoroughly every year, by removing (at simple
tank cleaning time), blowing them out with compressed air. If the handles are starting to get stiff....usually
that means at the every few years point I do the more thorough tank job ....I disassemble the petcocks &
service them. Almost never do I need any parts, other than a faint smear of silicone grease. Failure to
do regular tank cleaning is fairly likely to result in a rotted tank bottom....AND...a lot of junk getting
into your carburetors, or at least fuel screen(s).
4. http://www.chm.bris.ac.uk/motm/leadtet/leadh.htm has some interesting information on lead & MTBE
for gasoline. There are other websites that have considerable technical information on fuels, additives, etc.
There is a fair amount of information scattered throughout this article of mine, that covers leaded fuels:
5. Questions often arise as to whether or not the screen, petcock, lines, filter(s), etc., are flowing enough
fuel. This is easy to actually calculate, if you figure the worst case, such as 20 mpg at wide-open throttle.
But, here is a guideline of mine, that is perfectly adequate, & you don't have to play with mathematics:
If you have a small displacement airhead, such as a R65, you need a cupful of fuel flowing from EACH
carburetor, separately measured, bowl removed, common household 2 cup measurer underneath carburetor,
in one minute or less. For the larger displacement Airheads, a cup & a half or more is OK.
NOTE: fuel flow problems such as stumbling after a bit of cruising....can be caused by fuel
cap venting problems, not just clogged fuel screens and filters, etc. The fuel caps of ~ 1978
into 1979 were particularly susceptible to vent clogging.
6. Tank cleaning, coating, etc.: See http://bmwmotorcycletech.info/chemicalsetc.htm and
To clean a fuel tank, you must remove it. It is easier to remove the petcocks before you remove the tank
from the bike. I clean the petcocks/screens at the yearly tank cleaning time, & I may take them apart for a
more thorough cleaning & silicone grease lubrication of the parts. There are several methods for cleaning
the fuel tank. You might want to use the high pressure wand (soap mode, then rinse mode there or at home)
at the local car wash. If your local car wash uses non-phosphate soap ('environmentally safe, green, etc.'),
then do the entire job at home with a garden hose & common hose nozzle, a bit of dish detergent or laundry
detergent is good. NOTE!...if the tank cleaning is done because the gasoline, maybe some moisture,
whatever, has been in the tank & dried (mostly) from very long term storage, & probably looks like syrup
(or??)...then the tank should first be cleaned by adding a fair amount of some strong cleaner like Simple
Green. Use a 50-50 mixture & let it sit overnight. Then go about cleaning the inside with a pressure wand
of soapy water, then clean water, from the nearest car wash place. If all the crud does not come out, you
can either repeat the process, or start with chemicals. If your water pressure and nozzle is good, you can
probably do all these things at home. I use a siphon type gun, a gallon jug with hole in top cap for the
siphon hose, & my air compressor. The jug contains a strong detergent & water.
NOTE: One of the BIG reasons to clean an Airhead steel tank every year is due to condensed moisture,
which becomes water droplets at the bottom of the tank & will ROT OUR YOUR TANK. If you live
in an area where dew condenses on things, or your area is high humidity, this is exceptionally
important. I live in a very dry area, & still clean & then thoroughly dry my tanks, EVERY year. I
usually do the job during my Pre-Winter preparations for storage.
Note: The information presented in this section is GENERALLY for Airhead steel tanks. If you are
reading this & have a fuel-injection bike with the submerged fuel pump, be very cautious about using
harsh chemicals. Aluminum tanks can have problems from condensed moisture!
If you are thinking about cleaning and coating the inside of the tank, read this:
The rest of this section deals with relatively normal yearly or bi-yearly cleaning for Airhead steel tanks::
CLEANING: Remove the tank. Do the rest outdoors. Mix two tablespoons of common
(works better than "soap", particularly the no phosphates soaps) in enough warm water to fill your tank
at least 1/3 full (both sides of the tank). Don't fill the tank to the brim, you want plenty of room for
shake/sloshing. Shake the tank thoroughly. NOW remove the petcocks, and flush the tank strongly with
your outside-the-house hose (nozzle set for a somewhat narrowed but strong stream). This can loosen
& lift some old deteriorating red lining if vigorous enough, I don't find that a problem. Wash out the tank
thoroughly. For the petcocks you removed, flush them in all handle positions. DO NOT re-install them now.
The next step I recommend is to then treat the bottom area with phosphoric acid mixture (hardware
store screen door & other metals etching solution). DO NOT use anything except phosphoric acid mixture.
You will need cork or rubber stoppers to plug the petcock holes, & hardware stores also sell those.
I have tried several of these common low percentage phosphoric acid etching liquids from hardware
stores, they all seem OK. Low percentage phosphoric acid converts any remaining rust, even deep
into the bottom seams... & tends to very slightly seal the interior of the tank, especially the vulnerable
bottom seam area. Any bare steel areas, or rusting areas, will have a gray-colored look to them after
you treat the tank. That is a protective layer, although soft. It will take several hours of contact with the
etching solution...at least..... to do a good job. I do it overnight.
If you have never heard of phosphoric acid etching solution, perhaps you have heard of the jellied
form called Naval Jelly.
I am so anal about this (fixing/repainting a tank is COSTLY & if you do it yourself, it is a HUGE amount
of labor) that I put the washed & cleaned tank (& treated, if doing that) over one of my house heater's
floor outlets for a week or so, outlets downwards, cap off or open. No, it does not smell if cleaned
properly first. I do not do the phosphoric acid treatment EVERY year, as it is not necessary IF you
take care of your tank in refueling it (particularly in climate conditions where dew would form overnight),
& clean the tank yearly.
Rust-forming water accumulation is GREATLY reduced by refilling the tank before parking
the cooling Airhead overnight, where dew could collect INside the tank, if it is not full! The
dew collects, runs to the bottom in droplets; then you have water in the very bottom; & with
oxygen that gets in the fuel, etc., rust begins at the slightest microscopic place the tank,
especially the bottom, is not protected.
Be sure to have filters below the petcocks & clean the petcock screens yearly at least.
There are numerous tank coatings one can apply to the tanks; much more (VASTLY MORE!)
labor intensive products to use, compared to phosphoric acid solution. I don't like Kreem, Caswell's is
OK, as is POR15. A proper coating job is VERY labor-intensive (preparation), and if not done properly,
is a WASTE of all that effort, and can ...fast!....kill your exterior paint. I have had good results using the
vastly simpler techniques I describe here, EVEN on tanks that have the red interior lining flaking off.
The big problem with fuel tanks is not that some red lining peeling off from the tank walls....it is
deterioration at the tank bottom. It is water that is the worst offender. NO QUESTION that sometimes
one of these coatings like POR15 can be needed. Be SURE to prepare the tank properly...do NOT
SKIMP on labor...you will likely need to spend more time on preparation than the manufacturer of
the coating says.
****It is possible to use other products & methods to clean or treat the tank insides. You can also
use the reverse-plating method using sodium carbonate & water to fill the tank (obviously, first close
off the petcock outlets), then fit a big cork (OR?) to the top opening, with a piece of iron, rebar, etc.,
going through the cork & into the solution...but it does NOT touch the metal tank. Use a low voltage
DC power source to remove the rust. You can finish by using a zinc rod (maybe an old carburetor
bowl or pieces of one), & reversing the power leads. You will actually zinc plate the inside of the tank,
which is a very good protectant against rust. I suggest you look up this type of cleaning & plating via
an Internet search (Google.com is your friend here). Don't use the phosphoric acid method if you
plan to do this electric and zinc plating method.
SOME folks will purchase a small plastic bottle of gas or fuel-line treatment....the type that is for
preventing water from freezing in the fuel system of cars. This stuff is usually a very dry alcohol.
Some will clean their tanks with this stuff, using it as a solvent to wash the insides.....and to pick up
any water.....and they then drain it from the petcock area. This does work fairly well (for a cleaning)....
and no other solvents nor detergent/water nor acid treatment is done. If you are a regular tank
cleaner type of person this may work fairly well, although I am not so sure that it would not be a bit
harsh on the tank liner. But, I have some customers who have been doing it for many years without
major flaking. I'm not convinced it is a universal answer.
>>>>The method I use every few years on my own tanks is to remove the petcocks, thoroughly
clean what I can out of the insides with a strong detergent solution, preferably one that is NOT
phosphate-free, then flush it really well, corks into the outlets, and then put in a quart or so (pint
each side of tank) of common aluminum screen door, or galvanized flashing, etc., etching product,
various names, all containing a weak mixture of phosphoric acid. I let it sit from mid-morning to
afternoon, or overnight. I then remove the acid mixture & put it back in the plastic container for
another use (two or three times seems possible, depending on the amount of rust in the tank), I
flush the tank with water, then dry it as noted earlier over the house vent outlet, right side up, with
the air going into the petcock holes. Takes a day or three usually. The phosphoric acid is simply
a liquid form of naval jelly. It will convert rusty surfaces, generally to a gray color, & that colored
layer, thin & soft as it is, is protective against further rusting. It works well for this at the tank
bottom where the serious rusting begins & ends with holes, if you let it go. Yearly, clean the tank,
but there is usually no need to repeat the phosphoric acid, or not for a long time, typically several
years. This stuff is not a sealant/protectant like POR15, but it works well, & is hugely-vastly easier
to do. Try not to scratch the insides of the tank with hose nozzles, etc.
7. Alcohol in fuels (gasohol, etc.):
A lot has been printed, a lot said. It is bad for hoses & other parts including plastic types of gas
tanks. BMW has had bulletins out about the dangers & problems of using gasohol. We can't get
away from it in the USA. Below is a link to an article, for boaters with fiberglass tanks. It explains
a lot, if you read it thoroughly. I could cite a LOT of articles about problems from alcohol-laced
fuels. Just be aware, that even if you have a steel tank, the lining may be damaged over time, &
alcohol-laced fuels are likely to deteriorate MUCH faster & attract condensation of water easier
which rots the tank bottoms. In addition, alcohol causes carbureted engines to run leaner, unless
you change carburetor adjustments including jetting & needle position, ETC. Common old style
rubber fuel lines used on Airheads deteriorate faster. Same for lines on the injected K bikes.
Here is the article about boat tanks: http://www.boatus.com/seaworthy/fueltest.asp
8. Fuels, in general:
Summer & Winter fuels vary not only for miles per gallon, but for volatility, ease of starting, & the energy content
can vary up to about 7%. A GRAM of LEAD (as TEL) will raise the (R+M)/2 value of octane by about 6 numbers.
Pure hydrocarbon gasoline, NOT the type with any alcohol in it, can only hold about 0.15 teaspoon of water in each
gallon. In other words, water hardly dissolves in pure gasoline. But, if the gasoline has about 10% by volume of
Ethanol, a very common additive used for oxygenation purposes, then that fuel can now hold about 4.0 teaspoons
per gallon (assuming very dry gasoline & ethanol to begin with!). The problem occurs if just a bit more water is
introduced, even by overnight condensation, over time. The gasoline, water, & alcohol can then SEPARATE, &
when that separation occurs, water & alcohol sink to the bottom of the tank....which hardly does any good to steel
tanks, & might be hard on the engine if it gets into the engine. The fuel characteristics also change even if that does
RON specification, in layperson's terminology, is the specification most concerned with LOW & MODERATE
power usage; & for potential for engine run-on, also called dieseling. MON specification, in layperson's
terminology, is the specification most concerned with HIGH power operation (Knocking).
(R+M)/2 is a compromise specification.
Rule of thumb:
RON is USUALLY 8 to 10 higher than MON.
USA sold 87 octane fuel is approx. 82 MON; and 92 RON
Engines vary & most very modern engines with fuel injection now have the ignition automatically retarded & thus
the maximum power produced is lessened if the fuel's octane is lower than the designed-for octane....this is not
so for Airheads.
Here is a chart of the
MINIMUM NEEDED RON (remember, RON is perhaps 5 or 6 points HIGHER
than USA marked pumps which are (R+M)/2. So, the values below can be REDUCED by about 5 or
6 points, for what YOUR engine is LIKELY to need, for USA marked pumps. Keep in mind that your
engine LIKELY has a HIGHER compression ratio than its mechanical calculation...due to carbon buildup,
etc. Keep in mind also that RON is NOT done by the most stringent testing; RON is for low & medium
throttle/power settings. It is MON that is for high power output. Remember, that in the USA, RON+MON
divided by 2, in other words, an average, is what is on the USA pumps.
Compression Ratio Needed RON (for USA marked pumps, subtract about 5 or 6 points)
NOTE! The above chart is for a near perfectly machined, clean & smooth combustion chamber, under
near ideal conditions, & with single plug per cylinder ignition. For a dual-plugged ignition, might be best to
use the same figures & just know that the near perfectly machined & clean & smooth combustion chamber
no longer has such strict needs. NOTE that if your Airhead had a stock 8.2 CR, & you milled the head a
bit, & have a CR of, say, 8.8; then you need at a minimum, assuming jetting for BEST POWER (this is a tad
rich), USA marked pump fuel of about 87-88 octane. This tends to work out quite accurately....if you have
dual-plugging. It is marginal, but doable, with single plugging.
I've been asked about how much lead (TEL) was used in the leaded car gasoline's we used to have, years ago.
It was up to 2.4 grams per gallon. Aircraft piston engines had, generally, twice (or more).
PRESENT day Aircraft fuel is 100LL, & has about 2.12 grams per gallon.
There is a fair amount of information scattered throughout this article of mine, that covers leaded fuels:
There is a good discussion of compression ratios, head milling, cylinder shaving, ETC., here:
Fitting other tanks to your airhead; SEATS....etc....:::
Often someone wants to install a fuel tank or seat or both that is not the original version. There is often
confusion about what fits what, & what the PROBLEMS are, if any, when fitting some other tank or seat.
There were a number of various /5 tanks; see much further below.
Just before the disc brakes came out on the /6, BMW modified the underside of the fuel tanks to allow for the master
cylinder that was coming.
It is not at all uncommon to swap various tanks and seats.
The /5 and /6 SEATS are LONGER than the /7 seats.
The /7 SEAT will be OK with a /5 or /6 tank.
The /7 tank can fit a /5 or /6, but modifications are needed, otherwise it is rather ugly.
The 1973-1/2 (+-) tanks did have the underside cutout for the MC, but the MC did not actually appear until the 1974
models. The first disc brakes were the ATE brakes. There were two types, the swinging type, and a later fixed type
that looked somewhat like a Brembo, but with ATE's name on them. With the front Brembo brakes came the MC on
the handlebars. The reason for the bars Master Cylinder is that in the same era, the metal pad under the fuel tank
where the ATE MC had been mounted was then used for the ignition module. There are some variations.
A /7 tank will fit on a /6. But, best to use a /7 seat. In general...some tanks when substituted, depending on what
tank, will require, or might be nice, to have a shorter or longer nose on the seat. The seats themselves may look
similar at first glance, but may not be. As example, the /6 tanks have the mounting pins facing each other; the /7
and later are facing the rear. The later tanks have the hinges welded to the steel pan. The early ones had screws,
and you might have to unscrew them to get the seat on and off. Because of these variables, frozen screws, etc.,
many converted the seat to a LIFT OFF style.
Many questions are often asked about tanks. There were a LOT of variables, and although this is not information
pertinent to fitting them (note: all /5 tanks fit all /5)...here is some detailed information:
The standard capacity 6 gallon tanks had black knee pads.
In 1972 the Toaster tank was, however, standard for the U.S....withOUT pin striping.
Early in 1973 production there were not only the toaster chrome panels, but also pin stripes.
Rubber pads were available for the small tanks...AFTER the chrome panels were discontinued.
Authorities tanks (Police) look like the /6 tanks, with the rubber pads too....but the top has a lid.
/5 tanks have screwed-on Roundels.
1970-1971: a larger tank was available, and had either 6 or 6.3 gallons, the books are unclear as to
official value. In 1972-3 this larger tank was no longer stock, but a special order. I think a few were
produced that way for 1973.
1970-1971 fuel caps were hinged at the FRONT; 1972-3 caps were hinged at the REAR.
1973-1/2 (+-), had the underneath master cylinder cutout, which was to come in the 1974 models.
Standard tanks had black knee pads.
1972: "Toaster" tanks were STANDARD for U.S. shipped bikes. They had NO pin striping, and this tank
WAS available for 1973. the 1972 tank was about one gallon less capacity.
Early 1973 tanks had the chrome panels, but ADDED pin stripes, round the panels. There were rubber
pads available for the small tanks after the chrome panels were discontinued.
POLICE (Authorities) tanks look like the /6 tank, even have the rubber pads, but ON TOP there is a LID.
/5 tanks have SCREWED-on Roundels.
GS or R100R tanks WILL fit a R80ST, will add 5 liters.
R100GS tank WILL fit a R80G/S
A PD tank adds 6 liters over stock.
A GS tank, on a ST, needs rubber 16-11-2-307-014, plus fuel splitter and hose...or, block off one petcock
outlet. With this arrangement of GS on ST, will be a small seat to tank gap.
The early R90S had a 24 liter tank, with a RAISED filler cap.
YES, you can modify the later tanks with the flapper restrictors, to increase fuel capacity. Remove and
plug the crankcase downpipe in the starter motor area. You can remove all the solenoids, etc...too.
Do it properly. See my pulse air article for details: http://bmwmotorcycletech.info/pulseair.htm
With minor work, you can interchange these seats: R100S, RS, RT, from 1977-1984.
AND, R100 and R80, T, RT....from 1981-1984.
Seat dimensions: I have only one I've measurements for here:
1977 R100/7: 29" front to rear; 12-1/4" widest point; 10" from front lip to seat post.
There are further differences in how the various seats mount.
a. The /5 models and the /6 to 1976, had the seat pins on the subframe facing each other. You had to
REMOVE one hinge to remove the seat. Be SURE to put anti-seize on the threads!
b. The 1977 /7 "U.S." seat pins faced in the SAME direction, and used CLIPS.
c. Subframes from the /7 will fit PRIOR long wheelbase bikes.
Early seats had the hinge portion screwed to the seat, with allen screws, and if they rust-out, can be a bear to
remove them....making it a bear to get the seat off the bike. There are variations. It is not uncommon for the
area around the seat portion of the hinges to rot out, from moisture accumulation. This can be fixed by making
up small flat plates in a U configuration, and having them welded to the seat bottom. This CAN be done with
the upholstery intact, if wet cloths are used. It is a good idea to drill the recess area of these hinges in any
event, whether during welding repair...or stock....to allow any accumulated water to go downwards.
Use antiseize compound on seat screws.
Don't depend on factory printed information on the tank capacity. When BMW publishes a fuel tank capacity,
you ADD the tank & reserve amounts to get the total amounts. I mention this here because the literature has
gotten rather corrupted on gas tank volumes.
Because BMW has a month-long vacation shutdown (the factory is closed in August), a year model could have
been produced near the end of the prior calendar year.
10. Throttle and choke (enrichener) cables: This section is not concerned much with what cable fits what bike
with what handlebars. See your Dealership, and, see Anton Largiader's website on CABLES. But, here is some
information on LENGTHS, etc., that are not always easy to find. Lengths of BMW cables MIGHT be printed on
the cable sheath. USUALLY the cable assembly part number IS printed on the cable sheath.
32-73-1-242-135 528 mm long, for 40 mm carbs
32-73-1-454-584 1158 mm long
32-73-1-454-090 1130 mm long, and is the left cable on such as a 1989 G100GS
32-73-1-454-091 1165 mm long, and is the right cable on such as a 1989 G100GS
32-73-2-311-827 1143 mm long, and is the left cable on such as a 91-95 R100PD using 40 mm carbs
32-73-2-311-828 1178 mm long, and is the right cable on such as a 91-95 R100PD using 40 mm carbs
See www.siebenrock.com for more control cable information
There is an article that gets into the cables more in-depth:
11. Fuel hose:
Fuel hose is made in many sizes. For our motorcycles, fuel hose has been used in stock 'nominal 6 mm'
size; some have used 5/16" & 1/4" SAE American sizes. OUTSIDE diameters vary! American, SAE type
of hose may not fit easily into the crossover area of the airbox, if you have a crossover hose.
Just because a hose has a nominal inside diameter, does not mean it fits, installs, nor 'pulls off' the same
as other hoses. This includes hoses with the exact same size specification, & it includes 1/4" & nominal
6 mm hose which are almost exactly the same mathematical size. In other words, while size MAY matter,
it also may NOT.
Hoses vary in materials, & how constructed. The hose may remain on the spigot/nipple from friction of
the nipple ridges against the mostly unchanged inside diameter. It may remain on from the nipple ridges
& actually making very distinct depressions to match, on the inside of the hose. A fairly stiff hose material
can get some goodly ridges, & need a lot of force to remove the hose (unless you pressure the END of
the hose). Some fuel hoses are made of two types of rubber in the same hose, with distinctly different
Hoses made of the wrong material to match gasoline may SWELL, & may come off, or eventually split....
but, most fuel hoses seem to harden, over time. Some take many years to harden noticeably. I have done
plenty of hose testing, including very long term testing, & I posted a summary.
You CAN get away with most any fuel hose, for awhile. Just how long you want your fuel hoses to last
or how long before rubber particles start causing problems, or how original you want them to look.
You should consider if your selected hose is easy to fit....particularly if you have a crossover hose at
the airbox area.
Hoses should almost never be 'pulled off'. The old fabric covered hoses were made in at least two
types; some would act like the Chinese finger torture toy, if you pulled on them..., it got tighter & tighter.
several modern hoses are somewhat like that too; the hose tightens while pulling on it; until brute force
pulls the hose off...or breaks/damages the nipple. The PROPER method of removing a hose is to
have a tool on the petcock side (end of the hose), & push on the tool while gently pulling on the hose.
That eliminates any severe tightening of the hose. Hint: put a large 'fender washer' on the
spigot, before pushing on the hose. Then, when you want to remove the hose, you push
on the fender washer while the hose pulling force needed is vastly less!
The original silver colored braided outside fuel hose is still available, from such as Bing Agency in
the U.S. The new-style BMW black hose from your BMW dealership is a DIN specification hose, fits
better, particularly the cross-over at the air-cleaner housing, where American hose is too large in
diameter. Old Volkswagens used a fuel hose that you may find easily: it is a 7 mm ID hose
(x 2.5 mm wall). It was used on 60's and 70's, etc., VW's. The VW number is N-203571; sometimes
shown as N203571 or N-203 571. There are problems with modern fuels & fuel hoses. When
fuel hoses deteriorate, they often release almost microscopic particles of various rubber & other
compounds into the fuel, & these can cause problems with the carburetors, INCLUDING overflow of
the float bowls due to failure of the float needle & seat to fully shut off the fuel. These problems
have WORSENED over the years since ALCOHOLS have been put into fuels (not to mention
some of the nastier other stuff). It is not easy to find out what the INNARDS of the multiple layer
fuel hoses are made of. For K bikes, the fuel pump & some immediate hoses, are all INSIDE the
fuel tank, covered by fuel. That is an even worse condition; & SUBMERSIBLE hoses are A MUST
inside the fuel tank (besides the need for a FI pressure type specification).
In general, fuel hoses used to be made of nitrile rubbers, usually called NBR or acrylonitrile butadiene.
These can be softened & will deteriorate in the presence of alcohol. Another type of hose is EPDM,
which is ethylene propylene diene monomer. This hose will not stand up to most gasoline's, over time.
The best fuel hose for an Airhead USED TO BE, but it certainly does not look original, a
fluorohydrocarbon elastomer, (FKM), such as Dupont's VITON. It USED TO hold up for many dozens
of years, wouldn't harden appreciably. It came in various colors. I can no longer recommend that
hose due to changes in composition of pump gasoline's.
A hose material that did NOT pass my tests (various solvents, gasoline components, ETC...short term
& long term) is Masterflex "FDA Viton" 96412-D
Fuel hose for Fuel Injected bikes (K bikes) is special...see my K bike section of this website.
The best fuel hose I have ever tested is Tygon type F-4040A. Holds up to everything &
does NOT harden too much....even after many years of use. I've seen a few exceptions, and have no answers.
Want to cover it with braid? http://www.mcmaster.com/#catalog/121/848/=10oyb2k
02/06/2004: Add dell.htm
03/14/2004: add #4
10/08/2004: add #5
11/27/2004: add #6
10/28/2005: Expand #2
08/23/2006: Add information on fuels, CR vs octane, and much more.
11/04/2006: more TEL information
04/14/2007: Add #9
04/19/2007: renumber this article from 12 to 12A
06/25/2007: add item 10
11/29/2007: add item 11
01/07/2008: remove bad hyperlink for Heinrich items, was #7
02/18/2010: add more information on fuel hoses
02/16/2011: add link for more information regarding alcohol & fuel tank problems; adding previously
blank item 7... and a few minor other things.
07/21/2012: Remove recommendations for Viton hose; add Tygon; add Masterflex FDS Viton comment.
09/28/2012: Add QR code; add language button; update Google code; clean up article a bit & update article
with regards to alcohol & deleting mention of MTBE which is no longer used in fuels
04/23/2013: Add more hose information
08/01/2013: Edit tank cleaning section
01/21/2014: A bit more editing on tank cleaning methods; add caution about FI submerged pumps tanks.
07/21/2014: Review again the article-in-process file, final clean-up, final version clarifying cleaning details.
NO substantial changes.
09/02/2014: Revise section 9 on tanks extensively, incorporating information previously in another article.
12/22/2015: Revise meta-codes. Narrow the article. Increase font size. Clarify some details. Clean-up.
© Copyright, 2014, R. Fleischer
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Last edit of THIS page: Tuesday, June 21, 2016