Yes. What Jan said.

This almost seems to be a tank problem. Runs great on the ground, then in the air it starts foaming up, or the clunk line has a hole in it that "un ports" halfway through a flight...sends the motor smoking lean and pop goes the plug.

Re-do your fuel system. New fuel line throughout, and be sure it's well padded. It can touch nothing but foam or you're asking for these sorts of problems.