i have a L20B everything stock except headers,and a single 45 weber.the guy i got the engine from said he jeted the weber.but i don't thing he knew what he was doing.from idle(1000rpm)to (2500rpm) the throtle is good but if i stomp on it it sputters.and somtimes i'll hold the throtle to the floor and the engine wants to die.even on the road. if i want to pass half-throtle it sputters.i need help.what could be the reason for that.maybe i need work done to the head??or maybe somthing else??ingnition??thanks for your help