Well, one rule of thumb is temp. Try to keep the tem around 230-250 F. I generally try to keep the temp around 240F. You didn't say what type of fuel your using but gereal concensus says to stick with what ever fuel you ran it in with. Meaning if you started at 18% stick with it or if you want to change go to a higher percentage, never to a lower one. Also, keep it clean and clean your filter element and reoil after cleaning. Use after run oil when you put it away after bashing and for storage. Manufacturer says to put 3-6 drops in the carb. I also put about 2 drops directly into the head and rotate the piston a couple of times before replacing the plug. After run oil keeps the fuel residue from varnishing inside and is also a rust inhibitor. Last thing, i just learned this after converting to a non pull engine since it makes it easier to turn it over. Make sure the piston is in the lower portion of the sleeve. Just rotate the flywheel till it starts to get tight then back it off a little. This makes it easier to turn later on but also keeps the piston from deforming itself and the sleeve once the engine cools off and starts to constrict.
