I have a stock 2004 rmz250, when i let of the throttle it backfires. I believe there are stock jets right now in the carb. If i run the bike with the choke it runs a lot better and dose not backfire. I guess this means i am running to lean, what is the stock jet sizes and what size jet should i go up to. Could i just turn out the fuel screw, but i am worried about overheating if i don't have it jetted properly. I also ordered a 42 pilot, would this solve it how many turns out on the fuel screw should i go with a 42?