Did you check the clearance between the accelerator pump rod ? It must be set at between .015-.020, I usually set mine at .017 . It is a pain to set, you have to do it with the motor NOT running. Hold the throttle at wide open, then have someone push down on the rod and put a feeler gauge between the bottom of the rod and the pump. Then adjust the nut with the spring accordingly to get the proper clearance.