Air in primary fuel filter. After running a bit above 3000 rpm engine will surge (doesn't die) will run smoothly at lower than 3000 rpm then regain strength and surge again. Pumping up fuel bulb necessary to help surging at higher rpm. I have replaced all fuel lines with new, changed out hose clamps to screw type rather than clamp. bypassed all connections from fuel tank to bulb and bulb to fuel filter. Still getting air in top of fuel filter.