Bad Fuel Pump??

[Bushwacker]

There are potentially 2 separate issues here, both related to fuel starvation, but for several different reasons.

1. If the floats are set too low, the motor will tend to run lean (not good if you run premix!), even if fuel pump is good. If they rebuilt the carbs, hopefully they would have also replaced all the internal fuel lines too. Otherwise some crap from old lines could break loose and plug up the inlet needle and seat or jets on the newly rebuilt carbs!

2. If fuel pump is weak and can't match engine demand, then yes, motor would start to lean out/surge as soon as fuel level dropped enough. Low float level would just let this happen sooner.

3. A fuel restriction is between pump and carb, like a partially plugged needle valve, might act like a low float or weak pump, but fuel primer bulb would be hard. A fuel restriction upstream of primer bulb would result in collapsed bulb.

Don't know if this helps, but a fuel starvation or blockage problem shouldn't be that hard to find. Pumping the bulb when engine acts up might give you a clue as to what's going on.