How much fuel has gone through it? TS4 plug will help with tuning. What temp is the motor when this happens? Reset your needle settings to factory and start again. Never finish your tune on the box. If it runs perfect on the box, when you put it on the track it will be too lean. Set the high speed needle so the motor almost tops out at the end of the straight. Always stay a bit fat on the bottom. If the high speed needle is to lean, it can affect your idle and bottom end a lot. Check for air leaks and a sticky clutch as well. Nitro has a ton of variables and some are harder to find than others.