Mirror of /pweb.jps.net/~snowbum/fuelmiscl.htm

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Fuel system---miscl. section
INCLUDING tank cleaning methods; Premium vs. Regular; fuel additives. Fitting other tanks, SEATS, Throttle and Choke Cables, fuel hose, ETC.

NOTE: An extensive article on Dell'Orto's, covering all their carburetors, not airhead specific, is now on THIS website: dell.htm
It explains in great detail not just how the Dell'Orto works, but is applicable in general to all carburetors....and MIGHT be worthwhile for you to peruse, even if you don't have one of these carburetors, which was used on airheads ONLY on the R90S.

2. If you have a high compression ratio airhead (modified later type; or, 1979 and earlier type with stock high compression ratio), and 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 well 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, and 1/4 gallon or more is VERY common, sometimes closer to 0.4 gallon.

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 tad LOWER than for regular. THE ENERGY CONTENT OF FUEL VARIES WITH THE SEASONAL CHANGES OF THE FUEL! Therefore, I think it is likely that SOME premium gasoline's WILL give LOWER...OR HIGHER... gas mileage than a regular gasoline will.....assuming here that the engine will run properly on Regular grade gasoline in the first place. Winter gasoline tends to have rather volatile things like butane or propane in them...etc. In the West, California in particular, so-called oxygenates, such as MTBE (being phased out) and/or alcohol (being excessively phased in), are added to most fuels. These additions GENERALLY cause 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...and leaning will cause stumbling, etc. The fuel content for energy changes with temperature, if you are REALLY anal about knowing stuff.

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. With the aging of our fuel tanks, even with the in tank or in petcock screen filter, I feel that this filter is a must in the line just below the petcock. There is a very much more complete article on this website on the fuel filters, petcocks, etc: fuelfltrs&petcocks.htm

_{4. http://www.chm.bris.ac.uk/motm/leadtet/leadh.htm
will have some interesting information on lead and MTBE for
gasoline.

There are other websites that have considerable technical
information on fuels, additives, etc.}

_{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, and 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 and 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.}

_{6. Tank cleaning, etc:

To clean a steel tank, you must remove it.   You can
leave the petcocks in place or use cork or rubber
stoppers.   I often clean the petcocks at tank cleaning
time, and may also take them apart for a more thorough cleaning
and silicone grease lubrication of the parts.    I
do a basic tank and petcocks and screens cleaning EVERY
year. This means removing the tank and petcocks, swishing
some gas in it, and flowing it out the petcock holes...repeating
until nothing more comes out.

    On my own bikes, every few years, I do a more
complete job.   I will do the above cleaning, and then
use some common liquid household detergent....and water....just
like you would wash dishes with.....swish the tank well, and then
hose it out out really well, then let it drip dry an hour or
more. I then replace the stoppers (or petcocks used here
for that function), swish some 'etching' liquid....a rust
preventative/converter material, into the tank, then I drain the
tank after maybe an hour or three or even overnight (better),
flush it once more, and let it sit a day or two or more to fully
dry out.   I have tried several of these common
Phosphoric acid containing etching liquids from a hardware store,
they all seem OK. Phosphoric Acid converts any remaining
rust, and tends to slightly seal the interior of the
tank.   If your tank is a big mess to start with, you
may have to do it twice, and be more thorough about getting the
debris out of the tank in the first place. Once done
properly just once, and it is pretty simple, I find the tanks
tend to stop the deterioration to a great extent....and rust
usually is not much of a problem again, with yearly simple
cleanings.

If you have a very grungy tank to clean out, you might well
consider using a high pressure wand at a car wash stall, then
washing the tank out with plain water, and letting it dry out.
There are fancier methods of cleaning tanks. There are coatings
one can apply to the tanks. A proper coating job is VERY VERY
labor-intensive, and if not done properly, is a WASTE of all that
effort, and can ...fast!....kill your exterior paint. I have had
VERY 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 tanks is not some red lining peeling
off from the tank walls....it is deterioration at the tank
bottom. It is water that is the worst offender.   Water
accumulation is GREATLY reduced by refilling the tank before
parking the cooling Airhead overnight, where dew collects INside
the tank, if it is not full!

     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 it would not be a bit harsh on the tank liner.
But, I have a number of old customers who have been doing it for
many years without major flaking.}_{NOTE
that due to the age of our airheads, I am a firm believer in
using aftermarket paper filters BELOW the petcocks, and
maintaining the 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 the 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 and service
them. Almost never do I need any parts, other than a faint
smear of silicone grease. Failure
to do some sort of 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).
See the article on petcocks and filters   fuelfltrs&petcocks}

_{8.   Fuels, in
general:

Summer and Winter fuels vary not only for miles per gallon, but
for volatility, ease of starting, and the energy content can vary
up to about 7%.   A GRAM of LEAD 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.   The problem
occurs if just a bit more water is introduced, even by overnight
condensation, over time.   The gasoline, water, and
alcohol can then all SEPARATE, and when that separation occurs,
water and alcohol sink to the bottom of the tank....which hardly
does any good to steel tanks, and might be hard on the engine if
it, concentratedly, gets into the engine. The fuel
characteristics also change even if that does not happen!

RON
specification, in layperson's terminology, is the specification
most concerned with LOW and MODERATE power usage; and 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

While engines vary, and most very modern engines with fuel
injection now have the ignition automatically retarded, and 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 small chart of the MINIMUM NEEDED RON (remember, that 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.:::
Compression Ratio         Needed RON
        7.0                                    75
        8.0                                    88
        9.0                                    94
      10.0                                    98
      11.0                                  104
NOTE! The above chart is for a perfectly mechanically machined combustion chamber, and under IDEAL conditions!   NOTE that if your Airhead has a 8.2 CR, and you mill the head a bit, and 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 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).}

_{9.   Fitting
other tanks to your airhead; SEATS....etc....:::

Many a time someone wants to install a fuel tank or seat or both
that is not the original version.   There is often
confusion on what fits what, and 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. To
clarify:

..}..the 1973-1/2 (+-) tanks had the cutout for the MC, but the MC did not appear until the 1974 models.
The first disc brakes were the ATE brakes. There were two types, the swinging type, and a fixed type that looked like a Brembo, but with ATE's name.

_{With the Brembo brakes
came the MC on the handlebars, the under tank ATE MC area on some
models was then used, again on some models, for the ignition
module (1981+, not ALL models).

As an example here, 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, rather easy
to do, the seat to a LIFT OFF style.}Many questions are often asked about the /5 tanks. There were a LOT of variables, and although this is not information pertinent to fitting them (they all fit)...here is some information:
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.
1970-1971 fuel caps were hinged at the FRONT; 1972-3 caps were hinged at the REAR.
1973-1/2 (+-), that cutout, underneath, as mentioned above, appeared.
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.
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.}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.

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.
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
32-73-2-31--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

11. Fuel hose:
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 and fits better, particularly the cross-over at the aircleaner housing. American hose is too fat (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. It has a list price of maybe $14 per METER, but is available at half that, or tad less than half.

_{Revisions:

02/06/2004: Add dell.htm

03/14/2004: add #4

10/08/2004: add #5

11/27/2004: add #6

05/05/2005: hyperlinks

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}