stalling at 3000 rpm

[bones774]

hi all, regarding my 1988 350 ci mercruiser v8 w/Rochester 4 barrel.
after being winterized in fall and put in water over the weekend I'm having some troubles.
For the first 20-30 minutes when cold the engine works fine under load, after that upstarts stalling at the 3000 rpm mark. If I pull back on throttle it will run fine. If input it in neutral, no load, I can race engine right till wide open.
any suggestions? thanks

 

[alldodge]

Reving a motor in neutral uses very little fuel, doing the same rpm on plane needs a lot of fuel

If you can let it sit for a while and it will run again for 20-30 minutes then probably the fuel tank vent line. Air is not coming into the tank as fast as the fuel is being taken out.

If it will not run again at 3000 rpm no matter what then this would be other things.

 

[bones774]

Reving a motor in neutral uses very little fuel, doing the same rpm on plane needs a lot of fuel

If you can let it sit for a while and it will run again for 20-30 minutes then probably the fuel tank vent line. Air is not coming into the tank as fast as the fuel is being taken out.

If it will not run again at 3000 rpm no matter what then this would be other things.

Ok, thank you. Where is the vent line located and how will i repair/replace?
Thanks

 

[Scott Danforth]

your V8 will rev to 5000 RPM with only 2 cylinders firing. that indicates nothing as AD mentioned, you are probably running out of fuel.

if you crack your fuel fill cap and hear a sucking sound, your vent is plugged.

 

[bones774]

PS-Now that you mention it, i remember the previous owner telling me about that, it may have happened to him too.

 

[alldodge]

The vent line will be close by the gas cap or part of it. Look at the tank and it will have the gas fill hose and a smaller one. Follow the small one up to where it attaches.

As Scott said, if it stats doing it, slow and stop, then open the gas cap and listen for air being sucked in

 

[vetting]

What i've done in the past is pull the vent line from right by the tank and then blow through it. It should be fairly easy to blow through it. If its not then you old spiders and junk in the vent line which then creates a vacuum in your fuel tank under load.

 

[bones774]

ok I know the fitting on the transom. sounds good and thanks

 

[bones774]

I cleaned it this weekend and the boat works great. There was a little wire screen inside the fitting and I poked it out with screwdriver, now I have to replace that.
thanks all

 

[bones774]

so the boat has been fine till now, the same symptoms returned, tomorrow I will work thru it but any reason that its starting up again? could it be an insect nest regenerated? gonna just try blowing thru it a flex wire thru line, not looking to go back to gas tank and work back.
any different suggestions?
thankd

 

[alldodge]

Fuel pump getting weak or there is a restriction between tank and carb.
Fuel line could be collapsing

 

[bones774]

I'll take a careful look, thanks
PS-had a lot of water in bilge I had to pump out, any correlation? the bilge water I know was just a float problem but water came up to middle of oil pan

 

[alldodge]

the bilge water I know was just a float problem

I don't understand, there should be no water entering to begin with?

 

[bones774]

that's 2 weeks on the dock, cockpit covered. I'm a newbie but won't some rainwater get in here or there?

 

[alldodge]

that's 2 weeks on the dock, cockpit covered. I'm a newbie but won't some rainwater get in here or there?

Adding this statement with the prior one clears things up. First statement without this one leads me to think the boat is taking on water

 

[bones774]

gonna start new threAd on bilge problem, thanks

 

[bones774]

hi, the original fuel problem has returned intermittently. When I remove the vent line from gas tank connection the motor runs fine yet if I blow thru the hose from gas tank to transom fitting there is no obstruction.
any ideas?
thanks

 

[bones774]

hi, the original fuel problem returns intermittently. when I remove vent line from gas tank problem goes away yet when I blow thru hose from tank to transom fitting there is no obstruction.
any ideas? thanks

 

[alldodge]

Back to a weak fuel pump
Only way to check is put a fuel pressure gauge on it. Best way is a Tee fitting

 

[bones774]

Back to a weak fuel pump
Only way to check is put a fuel pressure gauge on it. Best way is a Tee fitting

but why does it work fine after vent hose removal?