I have a Fox 2.4. It has had 7 gallons of fuel ran in it when I recived it. The fuel was mixed 40-1 Klotz. I have put 4 gallons thru it mixed with penzoil air cooled 40-1. After the first gallon it started spitting black stuff all over my airplane. I retuned the engine an it is still doing it.(7400rpms xoar 20x10). Would the fact that this engine had burned klotz oil from the time it was new have anything to do with it.

Some of the guys i fly with use the same oil type an mix an do not have this problem.

Any ideas would be great..Thanks

You've probably just been running the engine too rich from the beginning. Too cold and it never seated the rings correctly. Try working with the needles a little.

It's possible, although extremely unlikely, that the cylinder was never properly plated, but it would be more than surprising too see it running much after the first couple of gallons had that been so. Iron rings on a bare aluminum cylinder would not last very long....

How many gallons does it take to break an engine in?

If it's run cold and rich it could take 50 and not be complete. Instead of honing the ring to match the cylinder all that's done with a rich mix in a gasser is the elimination of heat and friction, floating the ring. Thermal cycling is crucial to a complete break in.