Okay I'm alittle stumped here, I have a carbed hp500 in the boat. Motor has 35 hours on it. Last weekend the rear (closest to transom) accelerator pump diagram started leaking bad, completely blew out. So pulled the carb replaced both of them with new, same size blah blah blah... Took the boat out Tuesday ran it for 3 hours no issues ran the boat hard for over an hour ran great. Go today on a poker run. Get to the first stop and smell some fuel, pop the hatch and the rear diaphragm is gushing fuel everywhere... We had a small lake of fuel in the intake manifold valley. So immediately shut it down managed to mop up the fuel and got towed in ending the day. I know for a fact they were installed properly..

My question is what are the odds that a brand new diaphragm went bad? I am pretty positive the accelerator pump arm is adjusted correctly as 30 hours of flawless operation plenty of wot runs. Just bad luck or something I'm missing here? I have a black cloud that follows me so it wouldn't surprise me. Any suggestions would be helpful as if I can't see as to why the failure it doesn't inspire much confidence. Thanks

Just a guess, float level to high or needle and seat are not sealing.

doesnt have a 50cc arm on it does it?.040 clearance between the arm and the lever at closed throttle?

carefully check the float bowl gaskets are on correct..The gasket has a hole in it so the accelerator pump can pump fuel through the squirters..if any of the gaskets are on wrong or the little hole is blocked it will blow a hole in the diaphragm..

also look under the squirter,,theirs a little round bar stock with a point on one end which is soppose to keep the fuel in the squirter circuit,that could be frozen or stuck cloced which could also blow it.

Thanks guys, I'm pulling the carb off the boat now. I'll let you know what I find. Yes I believe it's a 50 rear.

my money is on what FIXX said about the little check valve under the squirter. todays fuel is crap and when it sits it turns into a sticky goo. I have rebuilt about 20 Holley's this year alone and almost all had a stuck valve under the squirter.

So, pulled everything apart, checked to make sure it wasn't bottoming out, that the check valve wasn't sticking the pump arm had clearance with the throttle plate closed ect ect. The diaphragm looked like a reject from the factory. The metal spring cup was deformed and the rubber diaphragm was split across the whole length of the pump. I replaced it double checked everything and it seems to be working properly. (This is the rear pump on the secondaries) Ran the boat last night 2 hours and seems to be fixed. Keeping a spare in the boat now for peace of mind.