86' 5.7L Merc power loss/surging

[SeaWeedCT]

I ran the boat (1986 Four Winns Liberator, 5.7L 350 , Alpha One) about 35 miles from Niantic to Block Island, the trip out was great, boat ran spectacularly. Today we came back made it about 17 miles and I began experiencing extreme power loss and surging, the motor died once. It fired up fine every time and I was able to jog back going from idle speed to lowest possible plane speed. It seemed like running at idle speed helped then allowed for a 15 min run on plane, about 18mph, then the surging and power loss would come back. I noticed my oil pressure gauge acting weird, it would drop then come back up, the temp was normal the entire time so it's not overheating. I'm thinking it might be my fuel pump on its way out. The boat is in very good shape and has a new Q-jet Carburetor from last season. Shes getting old but this is the first time I've had motor problems. Anyone have any ideas before I start tearing my motor apart? Thanks.

 

[SeaWeedCT]

Re: 86' 5.7L Merc power loss/surging

Bump

 

[rbh]

Re: 86' 5.7L Merc power loss/surging

it runs, it bogs down, then picks up, then dies.
then it starts back up?
new carb last year, does it idle well?
is your base gasket sucking in any air?
I think if it was an intermittent electrical issue there would be no bogging just go and stop.
rob

 

[o-jay]

Re: 86' 5.7L Merc power loss/surging

Sounds like a fuel delivery problem. The fact that it runs fine at idle and for a while at speed kinda sounds like the demand just eventually outruns the supply. I assume that if you tried to run it full throttle, you probably just increase the demand so drastically that it had no chance - used all the fuel it had very quickly. Could be a weak pump, and just can't keep the carb full when you're using it faster than it's pumping. 35 out and 17 back? All on one tank? You could've sucked up some poop from a low tank level and partially blocked you filter so fuel volume is decreased (water is poop also compared to gasoline).

I'd check all aspects of your fuel delivery before I started tearing motor apart.

 

[Blu]

Re: 86' 5.7L Merc power loss/surging

SeaWeedCT - My 86 with a 5.0 is doing the same thing. Surges when over 3000 RPM, but idles and cruises great. Did you find the problem? Thanks!