exactly this.
try a 7.5 or 8.5 PV.
make sure your accel pump linkage is tight against the pump arm. it should squirt as soon as the throttle moves.
if it's surging at a steady rate down the hwy, then either you have a vacuum leak or your jets are too lean.
if it's surging when you gradually ease into the throttle, then look at the PV.
if it's backfiring through the carb, then it's lean.
set idle mix when the motor is fully warmed up. lean each corner out gradually for the highest RPM. then idle it back down where you want it to idle...
