Today i was at the field, and I started my .40 engine after two weeks ago having a crash. I check everything and it seemed to be OK . the first thing I noticed different was to prime it I had to put my finger over the carb.. Normally I put it over the exhaust pipe.

Then I notice the engine had some kind of run on knock, with the carb close the engine would continue to run for 10-15 seconds or so. I removed the top of the cylinder cleaned it as best as I can , and tried it again but it still had run on knock.

I removed the tank and re-seated the top and reinstalled it then flew the plane twice. When I landed the first time and restarted the engine it would cut off when I closed the carb. the second time I over shot the runway and hit some bushes. Not enough damage to call it a crash but I was very curious.

Can some one tell me what the devil is going on with this engine please ?