Motorcycle Repair: dirtbike stalling, air screw, factory specs

Question
I have a 2007 kx250f. my bike will start, but only to stall within seconds. no matter if it is hot or cold it always stalls unless your constantly revving the bike. while going it runs fine, but at a dead stop it will die. the idol adjust seems to be no help because when i turn up the idol,it just makes the rpms act funny and makes the bike drive itself without turning the throttle. i have played with the air screw but no luck. the bike also back fires louder than a shotgun. if you didn't see me coming you would think someone was setting off fire crackers in the woods. i have a slip on fmf pipe, but i didn't think that would be the problem. any help would be appreciated, thanks.

Answer
Kyle, My middle son has a kx250f and it has a aftermarket pipe also. Heres what you might check.The valve lash is to tight. These bikes are noted for the valves seating up into the head and you lose the cam to shim bucket clearance. Get the valve lash set to factory specs again and recheck the carb jets to make sure they are clean. This should help.