I've never had to change the heat range of the plugs and I'd suggest you don't need to do so either. What I did find is that if I'm running a low or no nitro fuel that upping the nitro content to a fuel with about 5% more nitro helps with starting and getting even runs on cold winter days.

The important thing when setting the needle valve is to run it up to the peak RPM and then back off about 1/2 to 3/4 turn to a richer setting. This way when the model gets into the air and the RPM climbs thanks to the prop unloading slightly it will not be running too lean. Usually a rising and falling cycle of the RPM indicates a lean setting. Also setting the RPM back a little richer off the peak then holding the model up at a 45 to 60 degree nose up angle at full throttle is a good check to make sure the engine can still draw the fuel up to the carb correctly. A lot of models put the fuel tank too far back, too low or a combination of both. With the tank installed like this they might run OK while flat on the ground but during any sort of climb the engine leans out due to difficulty in drawing up the fuel from the now overly lower tank.


The other common mistake is to try running the engine on too big a tank. Again this makes it so the last of the fuel has to be drawn from too far back and down to ensure that the engine can get a consistent run through the whole tank.