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Mercruiser 3.0L problem.

KevinPP's Avatar
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09-07-05, 12:49 PM   #1  
Mercruiser 3.0L problem.

I have a `98 Mercruiser that has a problem running. It starts ok, and when its not under load it will rev OK (although it does backfire sometimes if you open it up quickly) As soon as I put it under load it will not rev past 24-2500 rpm. It just seems to choke itself. It doesn`t die but revs slow down to about 2000 and only pick up again when you bring the throttle back. I`ve recently had it serviced, and I`ve had an engineer look it at (out of the water) to try and locate the problem. It has had new plugs, the filters are new, the carb has been checked and the jets blown out (there was a small piece of rust but this obviously wasn`t the problem) The compression has been checked and is ok. The anti-siphon valve has now been replaced (it sheered off when I tried to remove it) Prior to us buying it a month or so ago it had been sitting for a year, but it was serviced after this and has been refuelled several times. This happened a couple of weeks ago but seemed to cure itself after I left the boat for a while. This time though it is here to stay. Has anyone got the faintest idea what could be causing it? Thanks.

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mrock's Avatar
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09-30-05, 09:01 AM   #2  
sounds like it could be bad fuel (best case senario!!)

Savannah Dan's Avatar

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10-07-05, 12:02 PM   #3  
Could be several things. Do you have a fuel/water seperator? If not, you need to install one. If you do, go ahead and change it out. Fill it 3/4 of the way with fuel, and put oil on the o-ring before you put it on. Go ahead and replace all fuel lines too, and clean the fuel screen at the carb.

How is your mileage? If it is sucking gas, a carb rebuild would probably save you a lot of headaches down the road.

Are the plug wires new? You should replace them every 3 years to be trouble free.

Check to see if the plugs have any rust or water on them. If the do, don't use the boat again until you pull the riser/s and manifold/s off. The can go bad in salt water in 3-5 years. Bad ones will allow salt water into the cylinders, and this can get ugly expensive real quick. Good luck with it.

harveje's Avatar

Join Date: Jan 2006
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06-04-06, 08:51 AM   #4  
Bad muffler bearing......
Either bad / old gas or carb needs rebuilt or both.
I had to rebuild mine, it done almost the same thing (s).

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