Mercruiser Fuel Issue ? 1993 7.4 L

I have a 1993 7.4l Mercruiser in a Bayliner 2556.

Built in gas tank. There is an 18” rubber fuel line from tank to water/fuel separator, then an 8” metal fuel line to the belt driven fuel pump. I am using both fuel outlets on the water/fuel separator. One goes to the main engine and the other to my 9.9 Yamaha kicker.

When first running, the motor runs great at all rpm’s. After 10 minutes of so at higher rpms’ (over 3000) the motor will bog down and it obviously starving for fuel. First visual is that the primer bulb on the Yamaha is collapsed so I presume I am not getting air. I removed the vent intake hose right at the fuel tank and it made no difference. I loosened the fuel separator filter and heard a vacuum release noise. The system filled with air, primer bulb released and all ran well for a few minutes then the problem repeated itself. I presumed the vent was plugged but when I removed the vent hose it did not fix the problem. I loosened the fuel tank filler cap to allow air into the tank and this did not solve the problem. The only way to fix the problem is too loosen the fuel separator filter.

Can you offer any suggestions to help solve my issue?

Thank you…
Rob

Re: Mercruiser Fuel Issue ?

Did you check the pick-up in the tank? Sounds like you got a hair ball or something stuck in there.

Re: Mercruiser Fuel Issue ?

The problem to me is..........

The 454 fuel pump creates a vacuum to SUCK the fuel from the boat gas tank.

What it is doing is sucking it from the outbard gas line bulb.

the bulb is or should be a one way "valve" so it will not allow gas to go backwards. That is why when you squeese it gas goes to the outboard engine not the other way.......

Also I agree there may be something going on at you boat main tank....

next time loosen the hose at the tank connection. If you hear/feel a pressure release then dig deeper into fuel tank......

You need to run a seperate line for the outboard from the tank. You could put a TEE where the anti syphon fitting is and plumb the anti syphon out of one side of the tee and the outboard line out the other side of the TEE.

That way one would have no influence on the other......