"Dead Spot" up to 1/4 throttle."misses""stumbles" upon acceleration up to 1/4 throttle.Will not maintain 1/4 throttle upon acceleration or at highway speeds at 1/4 throttle.Once past 1/4 throttle it runs like it was shot with nitrous..I have-Replaced vacuum piston,cleaned and inspected the pilot jet,main jet,needle,float needle and seat,accelerator pump diaphragm,adjusted float level to 18.5mm,tested the floats for bouyancy,checked for intake manifold leak,checked the piston slide for smooth travel,removed and cleaned the fuel tank,and replaced the o ring in the float bowl.What am i OVERLOOKING?