07 Phazer mcx turbo issues

[SUMMIT700]

My brother has a 07 phazer with a mcx turbo on it, sled runs good except for some ocasional backfireing and he has to ease into the throttle, If he hits the throtle too fast the sled stalls out. Any ideas or is there any common problems with these sleds?
thanks

 

[yamahajohnson220]

Sounds lean. Pull the plugs. Too much boost and these engines WILL detonate.