I have a novarossi rs12s1x engine that runs fine up to ~240 F any higher and it wont restart. The engine was bought new last year and is on its second gallon and has good compression when cold. Not sure about pinch status. Do I need a new piston/sleeve? A lot of racers posting here and at our local track run fine up to 300F.

fuel is a major factor in how your motor runs when its hot.make sure you use good fuel like byrons,rocket science,mugen,etc.

I run Dynamite race fuel 20%.
OS A3 or McCoy MC-59 plugs seem to help it run better at higher temps.
The only way I have found to keep it running is to richen it enough so it stays under 230-240F

THAT TEMP SEEMS ABOUT RIGHT.CHECK YOU GEARING.COMPARE TO OTHERS THAT RUN THE SAME CAR.ALSO ID GO WITH A COLDER PLUG OS 5