The Carburetor Shop LLC
204 East 15th
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carburetors manufactured after about 1935 and a vehicle that is mainly driven
at altitudes of sea level to 4000 feet, we suggest the following calibration
changes to use ethanol fuel: E-10
-lower float levels 1/32 from original specifications increase main metering
circuits’ fuel flow by 10 percent, increase idle jet diameter by 0.002 inch.
Additionally: Accelerator
pumps with neopreme skirts should be changed to those having leather skirts. Foam
floats should be changed to brass. Carburetors
with vacuum metering systems may need a recalibrated vacuum spring. Failure
to make these changes will cause the engine to run lean. A lean running
engine will run hotter than normal, and this can cause premature failure of
valves, warpage or cracking of cylinder heads, exhaust manifolds, etc. Also,
a hotter running engine can have more problems with “hot soak”, a condition
often mis-diagnosed as vapor lock. Vapor lock, while rare, is more prevalent
with ethanol-laced fuels. It should be pointed out that the engine will
probably run slightly cooler than normal AFTER the calibration changes have
been made due to the additional oxygen in the ethanol-laced fuel. There is
much chatter on the web concerning the use of neopreme-tipped fuel valves
with ethanol not holding up. The premature failure of fuel valves is more a
function of the manufacturers deciding, that “staking” the seat is an
unnecessary procedure, which added to the cost of the valve. Staking the fuel
valve seal seems to alleviate this issue completely. This should ALWAYS be
done when rebuilding a carburetor using a modern pointed-tipped valve that is
tipped with neopreme. We have not
seen issues with neopreme-tipped valves, where the seat has been staked. Ethanol-laced
fuels will also attack certain metals, especially aluminum. This is probably
due to the water solubility property of ethanol. Best advice I can give to
minimize this issue is to drive the vehicle more often, not allowing the fuel
to get old in the carburetor. It should
also be noted that, due to the higher octane of the ethanol-laced fuels; more
power is possible for those who care more about power than drivability and
fuel economy. E-85 is becoming a favorite fuel for many racers. For carburetors manufactured before about 1935: IT MAY
NOT BE POSSIBLE TO ECONOMICALLY RECALIBRATE THE CARBURETOR! The key is the style of carburetor. The airvalve carburetors such as the Schebler model S (Auburn, Cord, Duesenberg, etc.) or the Detroit Lubricators used on 1928 and earlier Packards, and others, use a tensioned spring to control the mixture. The only way to adjust is to hand-wind springs of a different tension using the method of trial and error. It is often much easier and less expensive to simply replace the carburetor with a more conventional unit that may be adjusted, especially if one is subjected to E-15. If one has a more conventional carburetor (no air valve) then the suggestions for post-1935 carburetors may be followed. |