Merc 500 slowing down

[tzambo]

I have a 1967 Merc 500 runs great just got the boat to trim up properly. I do have one problem once on plane after a litle while the motor just starts slowing down. I noticed that if I bring it back down to idle and hit the throttle again it runs just fine for a bit then does it again. Could this be fuel starvation?

 

[coolguy147]

Re: Merc 500 slowing down

overheating?

if not done so already lately i would replace the impeller though

 

[tzambo]

Re: Merc 500 slowing down

Impellar is new, and there is plenty of water out the tell-tale. It only happens when it's WOT. I ran the other day for about 3 miles at about 1/2 to 3/4s throttle for about 3 miles and no problem. So I think i can rule out overheating.

 

[Aqualift]

Re: Merc 500 slowing down

Check or replace the fuel pump diaphragm.

 

[coolguy147]

Re: Merc 500 slowing down

pump primer bulb at wide open if problem stop then check fuel pump and replace neseccary parts