1991 5.7 350v8 no acceleration after 2000 rpm - bogging out

[icegal20]

Upon acceleration boat won't go over 2000 rpm, looses power, cant get up on plane. Also a random clicking sound in the starboard water hose that comes from the thermostat. New fuel water separator and new manual fuel pump installed. Boat starts good and idles ok. Boat has full tank of fuel (however was stored with minimal gas over winter). Could an anti syphon hose cause this?

 

[alldodge]

Could an anti syphon hose cause this?

Could be
Is it a new to you boat?

 

[icegal20]

Yes. I just stopped in the local shop ND they suggested a carb rebuild. Said it could be the secondary pump in the carb. Will pick up a kit today. He said the anti syphon valve wouldn't let any gas get thru if it was that??

 

[alldodge]

Agree mostly the carb, but the ASV can get partially clogged. Dont know enough info to make a good guess yet.

 

[icegal20]

ok thank you!

 

[icegal20]

Agree mostly the carb, but the ASV can get partially clogged. Dont know enough info to make a good guess yet.

Could a little ' tap tap' on the valve possibly help lol

 

[alldodge]

Doubt it

 

[alldodge]

Ya know if you really want folks to try and help, we need more info

Is it a new to you boat?

If this is a new to you boat then there could be a whole bunch of things it might be

If it isn't and it "did run great" last season then might just be the carb. Could also be a few other things.

Otherwise kit the carb and if it doesn't help, come on back and give us more info, or toss more parts at it, your money and time

 

[icegal20]

Thank you!. Absolutely will give more info if carb rebuild is a fail. I appreciate this forum very much.

 

[icegal20]

Ok, I just reached previous owner. Carburetor was rebuilt last summer so only 20 hours on it if that. The boat is a 24 foot doral 1991 5.7 Mercruiser Model MCM 5.7 litre 350 CID Serial number 0D444494. So we are thinking not to bother with the carb rebuild. Was going to spray some 'tune up in a can' just incase something gunked up, but not if it's not advised. Boat starts good, seems to idle slightly rough but not bad, takes off ok but as soon as it hits 2000 rpms it bogs out. Doesn't stall but no power to get up on plane. I've changed the fuel pump, the fuel water separator, put some seafoam in gas (full tank), checked the fuel filter assembly (it's a paper one, and I have a new strainer type but hadn't put it on yet since paper one looked ok). Any advice is welcomed.

 

[jimmbo]

new manual fuel pump installed. Boat has full tank of fuel (however was stored with minimal gas over winter).

Yes. I just stopped in the local shop ND they suggested a carb rebuild. Said it could be the secondary pump in the carb.

New manual fuel pump?
Old gas can clog and gum up filters and carbs.
Other things...
Choke might not be fully open, which will prevent the Secondaries functioning on a Q-jet, as can incorrect assembly of the linkage involves during a rebuild.
Secondairy Air Valve can get gummed up and stuck and not open.
Fuel Enrichment(Power) system might be lean due to stuck piston
Unless the Carb is a Holley Double Pumper, there is no Accelerator Pump on the Secondaries.
Ignition might be missing as load increases, or Timing is not Advancing

 

[alldodge]

Ok, I just reached previous owner. Carburetor was rebuilt last summer so only 20 hours on it if that.

ok, prior owner rebuilt carb because it was having problems would be my bet. Found out what the problem was and sold it instead of fixing. That is unless you have been using it recently and all was good.

I would start with a compression test.
What pitch prop is on the drive?

 

[icegal20]

A

New manual fuel pump?
Old gas can clog and gum up filters and carbs.
Other things...
Choke might not be fully open, which will prevent the Secondaries functioning on a Q-jet, as can incorrect assembly of the linkage involves during a rebuild.
Secondairy Air Valve can get gummed up and stuck and not open.
Fuel Enrichment(Power) system might be lean due to stuck piston
Unless the Carb is a Holley Double Pumper, there is no Accelerator Pump on the Secondaries.
Ignition might be missing as load increases, or Timing is not Advancing

wesome thank you. Yes it has a manual fuel pump.

 

[jimmbo]

As in what, a Squeeze Bulb? Not needed on an I/O, except for certain types of Troubleshooting

 

[achris]

Yes it has a manual fuel pump.

Mechanical fuel pump perhaps?

How did the engine perform on the pre-purchase test drive?

I'd start with a compression test. Then check the timing (as well as initial, also the advance is advancing)...

Chris....

 

[icegal20]

Just as an update; I took the new fuel water separator off and dumped gas into a clear container to see if it had water in it. Appears to be fine, no water. Sprayed the carburetor well with carb cleaner. Let it soak. Took it for a drive. Did get up on plane as long as I was slow with acceleration. Drove around for 10 min with lots of power and handled well. Then brought it back to neutral and tried to accelerate again If I give it gas like you normally should it bogs out still. There is quite a tick in the port side in the top water hose. It's a random ticking noise. Oil pressure Guage seems to dance around a lot until boat is on plane and then levels out at 50ish. Didn't yet get the carb rebuilt since it had just been done. I'm not a mechanic, but pretty handy. I enjoy learning about boats and can fix quite a bit of issues now but open to any suggestions with this one

 

[Rick Stephens]

1: spraying carb cleaner on a carburetor is like squirting an IV on a patients head. Not useful.

2: That the previous owner *says* he did a carburetor rebuild means almost nothing. Did he use quality parts or chinesium kit? Did he have any clue what he was doing? Did his rebuild solve the problems he was experiencing then? The most common repair job needing repeat is a carb rebuild - happens all the time. All it takes is doing it too quickly, and maybe with crappy parts, missing a couple small details in a rush or in ignorance - just like spraying carb cleaner on a carburetor, very easy to assume it was 'rebuilt'. Carb rebuilds are totally unforgiving of missing a small thing like a dirty passageway or an off spec float height.

3: That a carb was rebuilt a while ago doesn't mean anything some months later. All it takes is a bit of junk in the fuel.

 

[jimmbo]

Rebuilding a Carb is more than tearing it apart, and replacing the Gaskets. It involves actually checking the Settings of New as well as Old Parts, and Linkages

 

[jimmbo]

Did get up on plane as long as I was slow with acceleration. Drove around for 10 min with lots of power and handled well. Then brought it back to neutral and tried to accelerate again If I give it gas like you normally should it bogs out still.

That should direct you to look at the Accelerator Pump Circuit(clogged passages, and/or discharge nozzles), and the Power Enrichment Circuit(power Piston Stuck). The carb is likely a Q-jet, not too hard to service, Most repairs, a even a lot of Cleaning can be done just by removing the Top of the Carb, with it still mounted on the engine. On one of my cars, the Power Piston had a habit of Sticking. I devised a tool that enabled me to grab it through the Vent Tube and free it up, with a bit of muscle, and copious amount of Power Tune sprayed in the Vent Tube. Carbon deposits were causing the piston to stick.