The "spiiting back" tends to sound like a lean condition. I agree w/ the other post though... lets get some spec's: Jets size, PV or blocked? If PV, what size? Had a vacumn guage on it yet? Hows the float levels? Next, does it have a secondary idle adjustment? If so, no more than 1.5 turns there... that can cause hesitations/burps. Fuel mix screws... how many turns out at present? Ok, I am done w/ all the questions. Get some info & see if we can help more.