jrockstuart
Elite Veteran
Location: Allen, Texas
| I did a crude side by side comparsion of 93 octane gasoline and Coleman fuel in my weed wacker. I filled the tank with one fuel, ran it, emptied the tank, filled the tank with the other fuel, ran it, and then repeated this a few times until I had made sufficient observations.
I felt that the 93 octane gasoline made the weed wacker engine run smoother, but the RPMs didn't get as high at full throttle as it did with the Coleman fuel. I could tell as soon as the new fuel hit the carburetor because the smell of the exhaust changed and the full throttle RPMs either went up or down.
It is my unproven hypothesis that the Coleman fuel explodes inside the cylinder much quicker than the 93 octane fuel does, thus forcing the piston down quicker. This seems to explain the higher RPMs I obtained with the Coleman fuel, and it also explains the somewhat higher vibrations I obtained with the Coleman fuel.
The exhaust sound between the two fuels was also somewhat different at idle with the Coleman fuel producing a more pronounced "snap" with each combustion cycle.
I love Coleman fuel for its physical properties. It doesn't stink when you get it on your hands, and it never creates varnish in the tank no matter how long you store it for. However I want my engine to run as smooth as possible, and overall power output is secondary. I think that using higher octane fuel (if coupled with a large enough fan to provide sufficient cooling) will help the engine to run smoother.
With these very simple Zenoah engines that have fixed magneto timing and fixed intake and exhaust valves, varying the burn rate of the fuel is pretty much the only adjustment we can make to advance or retard the timing. The ideal fuel would be odorless, store indefinitely, create good power output in the engine, run cool, and not produce any vibrations.
Someone with actual laboratory instruments need so run a similar comparsion bench test using a Zenoah engine, but instead just listening for differences, rather taking measurements in verifiable and scientific way using a knock sensor, a tachometer, and a temperature sensor to determine which fuel is really best. Otherwise this speculation and hyperbole will continue indefinitely.
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