Mercruiser 3.0 runs ok for a bit then starts skipping

[lshaddx]

I have a 1995 Marada 19ft inboard with a 3.0 Mercruiser i took it out 2 weeks ago and it ran good for about 45mins to an hour then starting skipping as i tried to acclerate we barely made it back to boat launch. Got it home drained all the gas filled tank with 93 octane changed plugs, changed the oil, and installed a new fuel filter. Took it out this weekend and same thing pulled boys on tube a liitle bit and motor starts missing. Let it sit in water and cool and it cranks fine and did a little better but as i tried to accerlate it done it again i am at a loss i am a decent mechanic but inboards are new to me any help with this would be greatly appreciated. Thank you.

 

[achris]

Hello and :welcome: to iboats....

As far as the engine itself is concerned, it's just a car engine. Everything is basically the same...

First thing you need to do is determine if the problem is fuel or electrical.

I would run the basic 'baseline' tests.... Compression, spark timing (your engine should have electronic ignition, so no points to worry about). You've done the fuel and filter, so we can rule those out. Next thing I'd do is a carb strip and clean (as it's now over 20 years old, probably not a bad idea anyway)....

Chris............

 

[alldodge]

Your wasting money buying 93 octane, 87 is all it needs

I'm thinking the carb needs some work

 

[Silvertip]

Or fuel pump not able to keep up with demand under load.

 

[lshaddx]

ok boat guys and gals so far ive: put in new plugs. drained out old gas and added new, installed a inline fuel filter, cleaned filter inside carb, changed oil and filter. Took boat out this past Sunday and it did great for about 45mins and started same thing starting to cut out if i applied throttle. I dont have the right tool to check fuel pump thats all ive got left to check on fuel side, but how it starts acting up after it gets warmed up is making me lean toward the coil being bad? What do youll think? Its got the 3.0L mercruiser Alpha one motor and drive. Any help is greatly appreciated.

 

[Rick Stephens]

Did you disassemble and clean the carburetor, install a kit with new gaskets and needle valve? If not then the main culprit to fuel problems is not yet addressed.

Yes, a coil cn get hot and start acting up. Unfortunately, about the only sure fire test is to replace it and see if the issue goes away.

Ric

 

[alldodge]

Sorry, but I should have read your first post closer and would have also provided the following other possible issues:

It will run fin for 45 minutes to hour then this starts.

When it does start this, open the fuel tank cap and listen for air to get sucked in. If you do hear air, then need to check the tank vent line, becuase its drawing a vacuum

Pull the canister fuel filter to see if its full of gas

The fuel pump maybe getting weak, so get a vacuum fuel pump gauge and make up a Tee fitting with fuel line and clamps. Pressure should be 3 to 7 psi throughout the rpm range. Might even be able to get a loaner from and auto parts store.

https://www.harborfreight.com/fuel-pump-and-vacuum-tester-62637.html

 

[lshaddx]

I have not put kit in carb yet I did put one it @2yrs ago but may need another one and thank you for suggestions and checking my vent that hasn't crossed my mind.

 

[lshaddx]

I did have a little time today and I do know my vent pipe is ok not stopped up or anything going to try to rent a fuel pressure gauge tomorrow after work to check fuel pump maybe at least if its ok will rule it out. Thanks to everyone for the advice it has helped a lot.