89 Mercruiser 3.0 starts skipping after 15-20 mins...

1989 Mercruiser 3.0 inboard. I have owned the boat for 13 months. Last year the boat ran great almost all summer. I did notice a slight skip before we put it up for the winter but only when under a heavy load or at a high RPM. This year we took the boat out and the skip has magically increased. Here is what happens...

Crank cold motor in water at boat ramp... runs/idles great.
Run motor up to 35-40mph on the water for first 15-20 mins... runs great.
Stop or slow down after 15-20 mins and then try to bring it back up to high RPM... slight skip/miss begins to become noticable.
As we continue to run the motor after the first 20 mins or so the skip increases for the next few minutes and then levels off to a point that we are basically running 5-10mph back to the boat ramp.

Here's what I have tried:

Replaced Points, Condenser, Coil, Plugs, Wires, Cap, Rotor... nothing has improved.

I have tried opening the gas cap while running... doesn't seem to help at all.

Any ideas about what to do next would be greatly appreciated!

Re: 89 Mercruiser 3.0 starts skipping after 15-20 mins...

Sounds like it might be running out of fuel, have you replaced the filters in the carb and fuel pump? Maybe sucking up junk from the fuel tank or other fuel delivery problem.

Re: 89 Mercruiser 3.0 starts skipping after 15-20 mins...

Thanks. I was leaning that direction after everything else failed to produce any results.


Before I get started, is there a recommended way of removing the gas tank and/or siphon tube? I am alergic to explosions and melted flesh. ;-)

Re: 89 Mercruiser 3.0 starts skipping after 15-20 mins...

sladerwilson said:

Before I get started, is there a recommended way of removing the gas tank and/or siphon tube? I am alergic to explosions and melted flesh. ;-)

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Depends if you can get access to the fuel tank, mine is below deck and royal PITA to access, some are above deck and easy to access. I had to cut a 6" hole in the deck and install a deck plate, to remove the tube from my tank...

I would run the engine off a remote tank (portable outboard tank) to verify you have a fuel tank issue, before messing with a below deck tank.

Re: 89 Mercruiser 3.0 starts skipping after 15-20 mins...

fishrdan said:

Sounds like it might be running out of fuel, have you replaced the filters in the carb and fuel pump? Maybe sucking up junk from the fuel tank or other fuel delivery problem.

Click to expand...

Replaced fuel line. Took out siphon tube from tank. Replaced fuel filter with a clear online type.
Still... same result... after 15-20 mins the engine begins skipping. Any other ideas???

Re: 89 Mercruiser 3.0 starts skipping after 15-20 mins...

sladerwilson said:

Replaced fuel line. Took out siphon tube from tank. Replaced fuel filter with a clear online type.
Still... same result... after 15-20 mins the engine begins skipping. Any other ideas???

Click to expand...

You did not mention a water seperator/filter.....if you do not have one, get one. If you have one change the filter.
If you can access the main tank check for water. Always use stabil ethinol treatment to prevent water build up. Had this issue last year in my 3.0 and water was the culprit.

Airshot

I was just curious if you had found a solution to this problem. I am having the same problem with my 3.0 and am pulling my hair out!