Ive actally never timmed my truck but 5 to 7 min. should be about right, I think. sorry i meant that it is running rich. Make sure that the glo plug is very tight and the manifold is sealed well. Also make sure the carb settings are correct. Look up the factory settings and go from that. Try to lean out the top end a bit, and richen the low end if you need to hold the rpms up to keep it from dieing otherwise lean it, only a small turn at a time. but make sure that you know where all teh screws were origionaly[:@] or you will be out like i was when i first had my truck.
Your only loosing a few min. but that could be harming your engnie, if you cant find the prob. then take it to your friendly neighborhood hobby shop. Good luck!