Many folks alternate with something like one tank of >100LL and 2 tanks of 93 octane auto fuel, assuming there's no detonation >problem on 93 octane. I'll probably do something like 1:4. Marvel Mystery >oil is supposed to help prevent lead deposits. And no, I don't own stock >in Marvel Mystery oil... >Mark Langford ++++++++++++++++++++++++++++++++++++++++++++++++++++++
My experience with auto fuel in the TriPacer for 500+ hours and the KR for 163 hours has been good. I use 87 octane only because of the lower compression of these engines and mix Marvel Mystery Oil at 4 oz to 10 gallon as recommended on the can. I also add from 1/2 to as much as 1 qt. directly to the crankcase at oil change. Any time I used 100LL it seemed to foul the plugs very quickly if the mixture was not leaned, even for ground operations. Some pilots will run with one tank filled with 100LL and one with auto fuel and use 100LL for takeoff, etc., but to me that does eliminate the problem with plug fouling, lead deposits, etc. If I were going to mix I'd be inclined to mix at maybe 3 or 4 to 1 directly in each tank but that would be a hassle. I use baby milk bottles to add the MMO as they are graduated in ounces so it's easy to add just the right mix. I've heard some mechanics say they can tell if an engine was burning auto fuel when they tear it down and say it will cause nothing but problems. One mechanic claimed he had an engine that only went 200 hours and had to be overhauled because of auto fuel. From my experience I'd say there were other factors involved but that is just a gut feel and I have no scientific data to back that up. The Tripacer ran for many years on a 4 to 1 mix and I ran nearly 100 percent auto for the 500+ hours I owned it. When I sold it this spring it had 2240 hours since overhaul. The compression and oil consumption remained constant for the last 500 hours. It is still running fine. I'm not sure how much more you could expect from an engine with whatever fuel you were using. Worst case, it didn't appear that MMO hurt anything and no, I don't own stock in MMO either. The 500+ hours that I put on the engine started with one very low time rebuilt and chromed cylinder which went through breakin with auto fuel. As always, your results may vary.......... Larry Flesner
