You should have some castor in your fuel. That engine has a nickel liner in it
and they are weak, it needs all the help it can get. It will run much cooler with
castor in it as well. PowerMaster is a real good fuel, it has 1/3 castor oil in it.

Jett Engines manufacturing recommends PowerMaster. You can get some good
castor at a motorcycle shop. I add some to break-in a new engine, in the nickel
liner OS Engines, and some extra in the four strokes as well.

Dave.