As with any ABC engine, three things are critically important:
1- Engine must come up to operating temprature fast. That means you fire it up, go to wide open and peak out the rpm's. Thats right, lean it out to max rpm's then richen it up to about halfway between 4-stroke break and max rpm's. This ensures that the cylinder heats up to operating temps to minimize the interference fit. If you don't do it this way, the cylinder/piston fit will be prematurly worn out of tolerance.

2- Heat cycling is important. Run it 2 or three minutes (wide open) then shut it down let it cool completly. do this for at least the first fifteen minutes of runtime.

3- The proper fuel. ABC's do not like all synthetic fuels and Rossi's being high compression do not like high nitro. All my Rossi's run best on zero nitro to 7.5% nitro, any more than that they tend to get finnikey. Oil- I have always had the best performance and longevity with 20% total oil, with that content being: 80% synthetic, 20% castor.

If you do not make your own fuel, I highly recommend Sig Champion fuel 5% nitro for this engine. My second choice would be Wildcat Premium Extra. I would stay away from fuels not specifying the oil content on the label or those that measure ingredients by weight.

Hope this helps, this is what has always worked for me.

Fuelman