If all else fails you might consider replacing the carburetor (weak link in Thunder Tiger Engines).

I HAD the .61 and finally gave up and sold it. I replaced the .46's carb and it ran pretty well after that. I still have two .36's.....the older runs great, but last night I had to go retrieve it two times out on the runway after powered landing. The newer one has frequent dead sticks in the air.......Never again Thunder Tiger!!!