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Eldon, Missouri 65026


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Use of ethanol in older vehicles


Many states have jumped on the political bandwagon of pushing ethanol; which may be EXTREMELY DETRIMENTAL to older vehicles. Without going into the politics and/or cost both fiscal and to the environment of using ethanol, this article is designed to help at least keep the older engines running with ethanol fuel. Since we are carburetor specialists only, we will not get into the necessary modifications for fuel tanks, fuel pumps, fuel lines, etc., and leave this area for other specialists.


Ethanol has less energy than gasoline. Gasoline has 117600 BTU per gallon, ethanol 67000 BTU per gallon.


The common mixtures AT THIS TIME are E-10, E-15, and E-85. The number after the E is the approximate percentage of ethanol mixed with gasoline.


To determine the EMPIRICAL energy of a gallon of mixture, one may use the following equation:


BTU mixture = [(Percentage ethanol times 670) + (percentage gasoline times 1176)]



E-10 BTU mixture = [(10 times 670) + (90 times 1176)]

E-15 BTU mixture = [(15 times 670) + (85 times 1176)]

E-85 BTU mixture = [(85 times 6700 + (15 times 1176)]




E-10 has 112540 BTU per gallon

E-15 has 110010 BTU per gallon

E-85 has 74590 BTU per gallon


For some unknown to me reason, possibly the different octanes (different burn rates) of gasoline and ethanol; the end result is less than the empirical formula would predict. That is, the use of E-10 basically cuts fuel mileage by about 10 percent rather than the 4 percent that would be predicted by the empirical formula. Use of E-15 is even worse. Mileage decreases seem to be an inverse function of compression ratio. That is, worse results will be obtained on low-compression engines than high-compression engines. It is my belief (opinion, not documented by testing) that these observed results are due to the very high octane (read slower fuel burn rate) of the ethanol. The lower compression engines simply do not burn much of the ethanol. Power is also down unless carburetor modifications and ignition modifications are made.


We suggest basically looking at ethanol fuel in a different light. E-10 should be viewed as a liquid containing 90 percent fuel, and 10 percent inert filler; E-15 a liquid containing 85 percent fuel and 15 percent inert filler.


Also, while the volatility of ethanol is less than that of modern gasoline, the mixture of the two seems to increase the volatility of both.


For 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.

E-15 - lower float levels 1/32 from specification, increase idle diameter by 0.003 inch, increase main metering circuits flow by 15 percent.

E-85 - nope, not going there at all, good luck to any that try it!




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:




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.