Ethanol Motorcycle

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A copper fuel preheater warms up the alcohol.
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Ned Doyle displays his ethanol motorcycle, a converted 1979 Harley Davidson.
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A thumb-operated gasoline pump aids in winter starting.

When one balances the “convenience” of owning an automobile
against today’s high fuel prices and–in urban
areas–limited available parking, it’s easy to see why
many people have chosen motorcycles as personal
transportation. Of course, the two-wheelers do have their
disadvantages (especially in poor weather), but as far as MOTHER EARTH NEWS’ alcohol researcher and seminar instructor Ned
Doyle is concerned, a “scooter” is the answer to
the gasoline crunch.

Quite naturally, then, between a desire to broaden his
range of alcohol fuel experience and the chance to
hit us up for free ethanol during the course of a yearlong
testing period, Doyle went ahead and converted his 1979
Harley-Davidson Sportster in an ethanol motorcycle, and the
results were, in a word, amazing. The aircooled,
61-cubic-inch engine–normally well endowed with both
power and vibration as a result of its
long-stroke, twin-cylinder design–immediately became
more “civilized” while apparently delivering greater
amounts of torque (Doyle attributes this to the density of
the alcohol fuel charge and its slow-burning nature, which
evenly distributes pressure on the piston head). The only
noticeable “trade-off” was a slight reduction in top speed
and a 7.8% decrease in mileage, both of which the
seminar instructor was content to swap for a smoother, more
comfortable ride.

Two other areas that showed marked improvement as a result
of burning the homegrown fuel were engine temperature and
oil consumption. Because ethanol has a high latent heat of
vaporization (as compared with that of gasoline), it
absorbs a good deal more warmth from the engine’s
manifold and cylinder heads–in the process of
changing from a liquid to a vapor state–than does its
more conventional fuel counterpart. The result is a reduced
engine operating temperature … a welcome bonus
which–especially in an air-cooled
powerplant–can result in longer periods between oil

Ned reported that the conversion process was a relatively
simple matter. “The first thing I did was to enlarge the
main jet to 35% over its original diameter, using a small
jeweler’s bit and a pin vise. Then I reamed the fuel
port in the idle circuit to about 45% larger than normal.
Both of these changes seemed to suit the bike’s Keihin
carburetor while burning 185-proof fuel. I also
found–through experimentation–that the
motorcycle’s response was markedly improved when I
decreased the length of the accelerator pump
stroke … thus slightly reducing the amount of
additional fuel injected into the carb throat when the
throttle’s cracked open, and thereby diminishing
liquid’s tendency to form globules rather than

“Further testing indicated that advancing the ignition
timing–a modification that’s normally a matter of
course for any alcohol-powered engine, because of
the fuel’s high ‘octane’ rating–had such a minor
effect on the vehicle’s performance that I readjusted the
setting to factory specifications.”

The remainder of Mr. Doyle’s research work involved rigging
up a miniature cold start system and testing the
effectiveness of a small fuel preheater. As a winter
starting aid (necessary when the temperatures drop below
45°F or so, because of the ethanol’s resistance to
vaporization in cold weather), Ned simply mounted a
plunger-type plant waterer inside a homebuilt canister
fastened to the frame of his motorcycle. From the outlet
nozzle of this thumb-operated squirter he ran a short
section of 1/8″ model airplane fuel line to a needle valve,
then routed a length of thin copper tubing from this
control to a small hole drilled in the wall of the
carburetor air inlet … taking precautions that neither
the opening–nor the tube inside it–interfered
with the movement of the choke plate.

Now, when the compact container is filled with gasoline, a
pump or two on the plunger will provide a starting “prime”
for the engine … and the amount of boost can be
regulated with the needle valve.

The fuel preheater was another matter. Borrowing ideas from
MOTHER EARTH NEWS’ experiments with her Chevy pickup truck, the researcher located a short
piece of copper tubing having an outside diameter
compatible with the inside dimensions of the
motorcycle’s fuel line. He then found a copper strap (about
1/2″ wide and 3″ long), formed one end of it completely
around the center of the tube section, and soldered the two
“penny metal” components together. Cutting the alcohol fuel
line in half, resplicing it to the two ends of the
preheater, and bolting the metal medium to a convenient
“hot spot” on the engine allowed sufficient thermal energy
to be transferred through the device to warm the fuel.

During more moderate seasons, Doyle found that the
preheater had little effect on performance or mileage,
but in cold weather its presence tended to
enhance the engine’s operation.

Naturally, some people may be wondering what long-term
effects the alcohol has had on the bike’s fuel system.
According to Ned, there was no noticeable deterioration. “I
did encounter a slight swelling of the O-ring seals when I
tried to reassemble the carburetor after a periodic check,
but they returned to original size when they dried out. So,
other than a minimal amount of white, powdery residue in
the carb float bowl and fuel tank, there seems to be little
problem with using ethanol … even though some of the
carburetor’s components are synthetic.”

The bottom line, then–at least as far as Ned Doyle’s
12-month experience goes–is that his two-wheeled
transportation adapted readily to “homegrown energy” …
so well, in fact, that it may never see another drop of