1974 Mercury 65 hp - runs fine 80% of time then bogs down

This motor will run fine for a while and then just bog down at WOT. Then I have to play with the shifter level up and down until it kicks in again. It seems like it bogs down when I hit a big wave, maybe jarring something. Anyone know what could be causing this? I have had the carbs professionally cleaned, replaced fuel pump diaphragm, replaced fuel filter gaskets, fixed leak in fuel supply line, cleaned out distributor, new spark plugs, cleaned connections on switch box, and unplugged coil wire to clean.

Thanks!

Re: 1974 Mercury 65 hp - runs fine 80% of time then bogs down

Sometimes the O-ring in a fuel coupler can fail to seal when under vacuum from the fuel pump, yet seall pressure from the primer bulb just fine. Same can happen when the fuel hose is 'flexed' during a turn or the trim is moved.

Test by temporarily installing a clear hose between the fuel pump and carbs, run the motor and watch for any air bubbles passing thru the hose. Flex or lightly push on the connector as if the motor was being turned/tilted to see if that causes any vacuum leak. If so, replace the fitting with a FACTORY fitting OR just do away with the fitting and run hose straight into the pump.

Be SURE to remove the clear hose once finished as clear hose IS NOT rated for fuel!

Re: 1974 Mercury 65 hp - runs fine 80% of time then bogs down

What is the fuel coupler? Is this the mercury fitting that attaches to the fuel supply line?

Thanks!

Re: 1974 Mercury 65 hp - runs fine 80% of time then bogs down

Yes that's it.

I'm a big fan of running the fuel hose straight to the fuel pump. If you use a portable tank, just have a coupler at the tank itself so you can remove the tank to fuel up.

Anyone kn ow where I can find a face plate for a 1974 Mercury 650? I am trying to fix up an old boat that belonged to my Dad. He passed away in December 2017. My older brother had the boat after Dad's passing, but he kept it out in the weather without a cover and where anyone could take parts from it. I have found some of the parts, but the cowling face plate is the last one.

7 year old thread. Closed.

The usual places - Ebay and Craig's List.