MODEL ENGINEERING TIPS > GAS ENGINE FUEL

Fuel selection for our engines can be a problem. Some use the same gasoline that is used in their cars. My friends and I have tried this, but it really stinks when burned in our model engines. This is probably due to the low temperature that these engines operate at (especially the hit-n-miss) and the somewhat rich mixture required by smaller engines. We came to the conclusion that it also carbons up the valves and spark plugs far worse than the camp fuel we had been using.

Most model engine owners are using Coleman Camp fuel with good results. My Plunket Jr. engine (not a hit-n-miss) has higher compression than many model engines and I noticed that it made some strange knocking sounds that were not mechanical, so I decided it must be detonation. Wondering what the octane rating is, a friend called Coleman and was informed that the octane rating is only 53. No wonder that it knocks! Knowing that methanol (used in may race cars) has a very high octane rating and burns clean, in 1999 I went looking for a source and found it at an automotive speed shop. My Plunket Jr. and PowerHouse engines love running on alcohol! Valves and plugs stay clean, and there is no more knocking, but cold starting can be somewhat difficult.

I continued using the Coleman fuel in my antique model hit-and-miss engines because they are lower compression and don't knock on the low octane camp fuel. Over time, I finally became disgusted at the fine lint particles in the Coleman fuel which was causing all manner of problems maintaining a proper needle setting over a period of time. I began filtering the fuel and installing in line fuel filters on my engines. One day while at a Walmart store around 1997, I noticed they had camp fuel called Ozark Trails on the shelf next to the Coleman fuel. I decided to try a can and see how it compared to the Coleman fuel. Upon checking, I discovered that it was clear as water and had no trace of lint particles. It ran just fine in all my hit-and-miss engines. I told my friends about the Ozark Trails fuel and they gave it a try. Now they use it too and we all agree that it even has a better exhaust smell than the Coleman.

One day I got to thinking about the fuels I was using. The camp fuel is easy starting but carbons the valves and plugs, while the alcohol burns clean but can be hard starting when the engine is cold. I wondered if I could blend the two together and get the best of both. I discovered that up to 30 parts Ozark Trails camp fuel will blend with 70 parts of methanol. Any amount of camp fuel over 30 percent will not mix and will stay separate. An engine will start just as easily with this blend as with straight camp fuel. After running the 70/30 methanol/Ozark Trails fuel for more than 100 hours, I found that the valves and plugs stay really clean. The spark plugs in my Plunket Jr. and PowerHouse engines run almost a frosty white, no carbon deposits at all! The fuel needle setting needs to be a little richer and a tank of fuel will not run quite as long as camp fuel, but this could hardly be of concern. The methanol raises the octane rating of the blend to a high level. I think it is the best of both worlds, as they say. Don't use these fuels in your lawn mower or car, models only!

Addendum October 2006 - I have been running the 30/70 fuel in my V-Twin engine since it was built in 2003 and also in my new V-Four engine. After many hundreds of accumulated total running hours in all my engines, I have found no negatives at all with this fuel blend, only positives.

Addendum June 2008 - Wal-Mart discontinued the Ozark Trails brand fuel earlier this year or late last year. If anyone finds a good substitute (not Coleman) please let me know. I am now running straight methanol in all of my engines. If you decide to use Coleman camp fuel, you should at least strain it through a couple of coffee filters to remove the lint.



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