always use a primer bulb sold by an engine manufacture ie: merc/Bomb/yamaha/ Zuki.... The primer bulb will rarely stay hard while the engine is running, you have to overcome what the engine is pulling to get the bulb hard, and once its pulls that fuel, its starts to go down, you're keeping the bulb under vacuum. I would normally go straight to the low pressure pump, but they actually give very little trouble. Pull the pump off the valve cover with teh lines still connected and pump up the bulb, if you have fuel leaking past teh diaphragm, you know the pump is bad. Easy way to test the fuel system is to buy a fuel pressure test kit, they sell them at the auto parts stores for a reasonable price. One thing most people over look on Zukes are the high pressure fuel filter, its not cheap, so it rarely gets changed. If its like most of the engines i work on, the vapor separator tanks needs to be cleaned out, fuel screen needs replacing and then retest, if it still acts up, high pressure pump.
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