Now some may disagree with this but I will put it out there it's a old trick we used in the auto industry back in the 70's for carbon I have done this for years and never damaged a motor yet while running at operating RPM and your air cleaner lid off, take a bottle of water and drip it into the carb not enough to kill the motor but enough to slightly drop the RPM what you are doing is steam cleaning your combustion chamber and also check your timing and point gap if they are off you will get pre ignition.