Mercruiser Fuel Air Lock "

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 from the fuel tank 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 Air Lock "

1 install a fuel shut-off for the yam hose and the engine hose at the sep. cant have 2 open hoses at the same time
2 inspect anti-syphon fitting at the gas tank
3 check vent from main tank