What fuel are you running? Some engines don't like running some fuels (the specific castor blends seem to play a large role).

My Rossi engines run fine on blue thunder or traxxas fuels, but run hotter that the blazes of .... when I use O'donnell regardless of carb settings. I know the trx 15 engine was the same way. If you're not using blue thunder or traxxas fuel, give it a try.