87 5.7 mrecruiser surging under load

[Lwarden]

I recently bought a 1987 Sea Sprite 225 nice solid boat owner told me the motor was rebuilt in 09 by a marine mechanic, this boat sat for 2.5 yrs out of the water, coverd and winterized. The boat starts,idles and throttles up fine on the muffs, took it out for its/my first sea trial and it still starts,idles and throttles up fine, at low rpm it runs smooth,once on plane it starts to bog and surge, between 2000 and 3000 rpms, if I try to throttle past 3000 it almost dies. So feathering the throttle back to below 2000 we putted back into the dock. Got it back home and removed the water seperator thinking it might be suckin sludge or water out of the tank, emptied it into a clean mason jar and there was nothing but clean, fuel. It acts as though it starving for fuel at higher rpms and only under load but on the muffs I can run it up past 3000 and it hums just fine with not a miss one. Any suggestion would help greatly...Thanks...Lee

 

[Failproof]

Re: 87 5.7 mrecruiser surging under load

Fuel or ignition. Dirty/plugged carb, dirty or incorrect or incorrectly gapped plugs, bad plug wire(s), bad cap/rotor etc......

 

[Lwarden]

Re: 87 5.7 mrecruiser surging under load

OK! herer's what I did, cleaned the fuel filter, the one up on the carburetor, found it half full of gunk/dried up stuff, cleaned it with carb cleaner and blew it out with compressed air, cleaned the air cleaner, sprayed out the carb throat. added some fuel system cleaner/dry gas in the tank, refilled the water fuel seperator and reinstalled. Took it back out on the water and it did seem to run better but still at 3000 rpm it bogs if you continue to throttle up it seems to shut down, throttle back to below 3000 rpms and it comes back. Im still thinking its a fuel issue, like its starving for fuel at higher rpms. I tried to check/clean my dip tube but I cant tell how it comes out of the tank it sits just ahead of the engine compartment under the floor and I have to access it from the front of the engine compartment, I took the elbow off it and cant seem to figure out how to get the rest out. Im thinking at this point its maybe something in the fuel tank getting sucked up and blocking the dip tube. I think I might try connecting my portable outboard tank to the engine and see if it still runs the same...what say you oh mighty mechanics???????

 

[Lwarden]

Re: 87 5.7 mrecruiser surging under load

The plug wires,cap and rotor all look brand new, not to say their not bad but Im not thinking sprak issue here. It runs to smooth not in gear. Just an FYI, there was a point at which I had it planed out and hitting 3500 rpm and seemed to run smooth but wasnt long and it started bogging and was back under the 3000 rpm mark. Its gotta be fuel or carburetor Im thinking?

 

[Failproof]

Re: 87 5.7 mrecruiser surging under load

What carb? Sounds like its leaning out at speed. Could be fuel delivery, probably carb though.

 

[Lwarden]

Re: 87 5.7 mrecruiser surging under load

What carb? Sounds like its leaning out at speed. Could be fuel delivery, probably carb though.

its a 4 barrel carb not sure the brand

 

[Lwarden]

Re: 87 5.7 mrecruiser surging under load

how can I tell what carburetor is on it?

 

[Failproof]

Re: 87 5.7 mrecruiser surging under load

Picture of the carb will help. Any numbers on the carb? Post them here and that will help.

 

[Lwarden]

Re: 87 5.7 mrecruiser surging under load

ok took the Carb off and its a rochester quadrajet, so I took the serial nimber and went and got a rebuild kit and rebuilt it.. wont know if its any better till I run it this week on the lake.

 

[Bondo]

Re: 87 5.7 mrecruiser surging under load

ok took the Carb off and its a rochester quadrajet, so I took the serial nimber and went and got a rebuild kit and rebuilt it.. wont know if its any better till I run it this week on the lake.

Ayuh,..... Welcome Aboard,... What did ya find in the old fuel/ water separatin' filter,..??

What's the fuel in the Tank look like,..??

It'd be a shame to pump that rebuild carb fulla crud....

 

[Lwarden]

Re: 87 5.7 mrecruiser surging under load

We pumped 5 gals of fuel out of the tank straight off the bottom and it was all crystal clear, we did empty out the fuel/water seperator and it was clean also. Before we rebuilt the carb I did find quite a bit of crud in the inline filter at the carburetor housing. So we installed a new fuel pump on it and it runs like a champ about 4600 rpms WOT I think thats pretty good for a 3500 lb boat with about 400 lbs of people in it! So after all this it came down to a fuel pump.. what really set it in stone was the fact that the boat would run awesome on my outboard motor fuel tank as long as the primer bulb was always hard/pumped up. Made me think the old fuel pump just wasnt pumping enough fuel at higher throttle.

 

[Bondo]

Re: 87 5.7 mrecruiser surging under load

We pumped 5 gals of fuel out of the tank straight off the bottom and it was all crystal clear, we did empty out the fuel/water seperator and it was clean also. Before we rebuilt the carb I did find quite a bit of crud in the inline filter at the carburetor housing. So we installed a new fuel pump on it and it runs like a champ about 4600 rpms WOT I think thats pretty good for a 3500 lb boat with about 400 lbs of people in it! So after all this it came down to a fuel pump.. what really set it in stone was the fact that the boat would run awesome on my outboard motor fuel tank as long as the primer bulb was always hard/pumped up. Made me think the old fuel pump just wasnt pumping enough fuel at higher throttle.

Ayuh,.... Sounds like yer headed the right way,.... Good Luck with it, 'n keep Us posted,...