Country: United States
Date: January 2009
Hi, we hope to create an E85 mixture
using the ethanol we produced to power a two-stroke carburetor lawn
mower engine. Do you have any specific research or information about
rebuilding a lawnmower engine (specific parts, guides, etc) and the
adjustments that need to be made in order for it to operate on E85 fuel?
I don't have any of the engineering considerations for converting
gasoline to E85, although I'm sure you can find that on the Internet.
However, I have a more "global" idea for you to consider. Despite the
political pressures, ethanol has not and will not serve as a biofuel
in the long term. The production of ethanol whether from corn or
sugar cane depends upon the availability of water, either from rain or
irrigation. No water, no ethanol. Water is not a stable resource, so
neither is ethanol. Perhaps you and your class should sustainable
energy resouces. I pose the challenge, I don't have an answer.
Ethanol is a rather poor fuel to use in an internal combustion engine.
One problem is that ethanol contains much less energy per liter than
gasoline does. So for an ethanol-powered motor to produce the same
amount of power, it must use about 51% MORE ethanol than it would use
if it running on gasoline. The situation is almost as bad when using
E85, since E85 is 85% ethanol!
In addition, the fuel-air ratio of a motor using ethanol (or E85) must
be made more "rich" in order for the motor to even run at all. A
gasoline motor runs best when there is about a 14.7:1 ratio (by
weight) of air-to-fuel. That means that for every gram of gasoline the
motor uses, there must be 14.7 grams of air "inhaled" to burn the
gasoline with. When burning E85, the air-to-fuel ratio must be 9.76:1
Since the amount of air a motor "inhales" when it runs remains
unchanged (no matter what fuel it uses), the lower fuel-to-air ratio
for E85 means that the motor must use a lot more E85 than gasoline.
Now to your question: If you just poured E85 into your lawnmower
motor, it would most certainly run very poorly (and may not even start
at all). The carburetor must be modified to allow a lot more E85 to be
fed to the motor in order to get it to run properly, because you need
to feed much more E85 to the motor to make the correct air-to-fuel
ratio. It is unlikely that you will be able to modify the carburetor
for such a large change in mixture ratio. The carburetor was designed
to use gasoline, and cannot feed enough E85 to allow proper operation
without making large (and very difficult) internal modifications to
Now a couple of observations. It seems odd that you are trying to
experiment with what I assume you hope is a "cleaner" fuel, with a 2-
stroke motor! Small 2-stroke motors are terrible polluters. One lawn
mower motor actually produces as much pollution as 20 to 30 modern
Most importantly, E85 is not particularly environmentally friendly.
The production of ethanol results in large amounts of CO2. The CO2
comes from the fermentation process, and also from the fuel used to
heat and distil the ethanol. In a report published in Scientific
American some time back, it was stated that comparing ethanol to
gasoline, and taking into account the manufacturing processes and the
poor fuel economy of ethanol, using ethanol generates almost as much
CO2 as using gasoline would, if natural gas was burned to provide heat
for the industrial distillation process. However, if coal was used for
fuel in the distillation process (as it is at many ethanol plants),
using ethanol actually produces more CO2 than using gasoline! It is
becoming clear that using ethanol for fuel is not, at this point, a
viable solution. Sometimes, things are not as simple as they seem!
Hi, Alisha. Depending on the make of your engine, you can get very
good books about them relatively inexpensively. Search amazon.com or
Google for 'small engine repair briggs' (for a Briggs and Stratton) or
'small engine repair Tecumseh' (for a Tecumseh), varying the text
depending on which make your engine is. I have a detailed Briggs
manual written by 'Clymer's' if that helps with a place to start your
searches. If you need parts, you can get them from most any lawnmower
Are you sure it is a two cycle (also known as a two stroke)? Most
lawnmower engines I am familiar with are four cycle or four stroke.
Two-strokes are usually smaller, and are used in string trimmers and
such, though I don't doubt that there are older lawnmowers out there
that use a two-stroke.
As far as adjustments for a gas engine to run on E85, there is usually
no adjustment required, although you may determine the carburetor
should be adjusted a bit leaner or richer to get that particular
engine to run at its best. Lawnmower engines usually have an
adjustment screw in the carburetor for this. One thing you may want
to check is to determine what materials the o-rings and gaskets in the
carburetor are, and check to make sure they are compatible with
If it is a two-stroke engine, you will probably get the E85 to work,
but your reduction in pollutants will be minimal, because two-stroke
engines require oil to be mixed with the fuel. I know of no
experiments that have been done using a two stroke, but that just
means you will be doing something nobody else has. That also means
more work, but possibly more fun with the experiment, too.
The oil mixed in the fuel is to lubricate the engine's moving parts,
and you may need to vary the amount used in the mix to get it to a
good amount for use with the E85. Determining this amount may involve
repeatedly tearing down the engine to check how quickly it is wearing.
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Update: June 2012