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