20 hp mercury stalls

[mikec03]

It's a 1976, 20 hp outboard. The fuel pump has apparently failed. It is integral with the carburetor. If we pump the bulb, it will keep running, otherwise, the motor stalls after 5 min or so.

We have the pump rebuild kit, BUT there are two fuel check valve sheets in the kit [along with the gaskets and diaphragm], one phenolic and one rubber. The blow up drawing shows only one check valve sheet. The one that previously was in the fuel pump was phenolic but that doesn't seem right. How can a phenolic check valve seal?

Does anyone have an explanation?

 

[7920hpMercury]

Re: 20 hp mercury stalls

This is always confusing to me too.

And the Merc manual is not clear either.

I always put the rubber check valve one next the fuel pump body where it needs to seal and put the phenolic check valve one next to the gasket. So, I use both of them back to back. And it always seemed to work like this for me for many carb rebuilds. I also think you could likely use either one alone with success too but I never liked having left over parts!

Good luck!

 

[mikec03]

Re: 20 hp mercury stalls

Thanks for the reply. We installed both the check valves with the rubber one next to the pump body as you suggested and the outboard ran OK for about 30 min.

We will be taking the boat out on a big lake where we will be camping for a week so it's real important to get this right.

By the way, a local Merc dealer mechanic said that some motors use the rubber one and some the phenolic one! I don't believe this, but I'm still wondering at the logic of having two check valves in the rebuild kit?