1990 XR600R If I was to install an aftermarket free flowing: air filter and muffler, (which would bring a lot more air into the carb/engine, correct?), would I need to rejet my carb and bring in more fuel to compensate for an increased amount of air going into the combustion chamber? I would think that I would have to rejet the carb otherwise the engine would run to lean and overheat, correct? In order to rejet the carb on a 1990 XR600R, would you buy new jets and replace the old ones with them, or would you drill the current ones out to a larger size? If your engine is backfiring, that is a sign that it's running to rich, correct? Because un burnt fuel is exiting through the exhaust pipe and igniting in there.