RE: Jett .35 RPM range (new)
Did you run it first on your own test stand when you got it back to get baseline measurements ???
From the images it looks like the sides and back of the tank are a tight fit. But hard to see.
Blackened or carbon means little. Plugs blow 95% of the time due to a lean run.
I will recommend using omega fuel. Or add 2 oz of castor to the cool power.
Bob