3.7 Mercruiser engine problem

[Wayne in MO]

First time boat owner (purchased late last year), 1989 Celebrity w/ 3.7 mercruiser 165 HP. After running for about 30 minutes, it starts backfiring and popping through the carb. Once it dies, I can restart, and it will idle, but once I put in gear, bogs down and dies. I have replaced fuel with 100 octane, have put heat in the fuel to eliminate water, replaced distributor cap and rotor. I thought it was the electronic ignition kit that I put in, took back out and put points back in, and still get the same thing. I have replaced plugs, plug wires, and coil. Mechanics don't run it long enough for this to happen, and say they're not sure.
Any thing else I need to look at, or any suggestions would be greatly appreciated.

 

[dry dock]

Re: 3.7 Mercruiser engine problem

might try fuel filter-fuel pump i had a simular problem and i added a eletric fuel pump solved my problem good luck...........

 

[Bifflefan]

Re: 3.7 Mercruiser engine problem

Sounds like an intake valve sticking open. Possible its has an oiling problem or a valve stem that is expanding in the guide. Start is up in the driveway on the hose and let run until it does it, then shut if off and do a compression check. Ill bet you find a low hole only when its warmed up.
You may need a head rebuild.

 

[Wayne in MO]

Re: 3.7 Mercruiser engine problem

Already changed fuel filters (there are 3). Cannot get it to do this on the hose in the driveway, only on the water, after running it under load for about 30 minutes.

 

[missalot]

Re: 3.7 Mercruiser engine problem

Take a look at your fuel tank vent too, mud wasps did a number on mine a while back.

 

[Wayne in MO]

Re: 3.7 Mercruiser engine problem

Funny you mention that. Mechanic found dead wasps and bugs at the check valve. Cleaned everything out...and have a screen on the fuel tank vent too.

Another thing I should mention is that the boat never had this problem until mechanic put a new check valve on it.

 

[Wayne in MO]

Re: 3.7 Mercruiser engine problem

Duplicate post

 

[Blk-n-Blu]

Re: 3.7 Mercruiser engine problem

Try running with the gas cap off and see if that helps.

 

[Wayne in MO]

Re: 3.7 Mercruiser engine problem

I see a lot of posts here recently with the similar problem. Think I will replace the coil and see if that does anything.

 

[Wayne in MO]

Re: 3.7 Mercruiser engine problem

Took the boat out for a spin 2nite, still had the same problem with it popping threw the carb. I was running at about 4400 to 4600rpm when it was popping, I idled back to 4000rpm and the boat seemed to do fine. I've been told I could have a valve problem or the circuit board on the side of the motor might be shorting out. Would the tipe of oil im using have anything to do with it?(10w40) they were runnig 25w50

 

[dirtdiver]

Re: 3.7 Mercruiser engine problem

I had the same problem with mine. It was the springs on the counter weight under the points. Check to see if those are sticking.