Kirch

This is a post for a friend whom I'm helping with a fuel pump problem. Ok here's the deal, it's a 98 Merc 502 converter to a 502 blower motor with dual carbs. Makes about 700HP.

This weekend we were out boat running fine and smelled gas. Come to find out the vent line from the pump to the air air filter came off and was spraying gas all over the place. We were told that the vent line shouldn't have gas coming out it unless the pump was bad. So we took out the pump and sure enough the diaphragm was torn causing gas to pour out the vent line. No big deal to fix right? So 7 marinas later we find a fuel pump for a 502. However, his original pump had tapped fittings to accomidate the larger stainless braided lines. So we decided to swap the guts of the new one with the old one and use the old housing due to the fact we didn't have a tap. We put the pump back in and it wouldn't even start. Mind you the boat was running fine before, it was just sparying gas in the engine compartment. I even took the feed line off the carb to see it was pumping gas and nothing. So I though it might be air trapped in the line. So I took the feed line off the pump and filled the line with gas attempting to purge any air....... didn't work. So I take the pump off to make sure the level is in the right position...... it looks ok.... it's wearing in the same position as the old one. So at this point I'm scratching my head. Again, the boat ran fine with the old one it just sprayed gas out the vent hose. Is there something we are going wrong? Do you have to prime this pump somehow or purge the air???

Also, what would cause the diaphragm to tear? I noticed the metal disk above the diaphragm was bent on both sides like it was extending too far..... that would have pinched the gasket. However, why would it extend that far???

Any thoughts would be great.

Cord

I used to have a quadrajet in a car. The quadrajets are notorious for having internal leaks. Well, if the car sat for a week, the carb bowls would be empty and would need to refill before the engine would start. This would take a good 30 seconds of continuous cranking. Mind you, the fuel tank was almost level with the pump, not below as with a marine application. My question is if you spun the motor long enough to reprime it.

Kirch

We cranked on it for quit a while. I even took the feed line off the carb to see if it was even getting gas up to the carbs....... and nothing?

Cord

Ok. Some manufactures put a check valve in the supply line to prevent siphoning. Does he have a check valve?

BTW-has he check the oil level? In automotive applications, the fuel pump is open to the crankcase, so usually the oil is dilluted with fuel. Not sure about marine apps because of the extra vent line.