3.0 mercruiser losing rpm's after warming up

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bake415

Recruit
Joined
Jul 11, 2004
Messages
3
I have an 3.0 1997 mercruiser freshly tuned up that runs excellant ...till it has been ran for about 15 minutes then it starts to slowly lose rpm's. Its goes from 4200 rpms to 3500rpms at wot.
 
WillyBWright

WillyBWright

Fleet Admiral
Joined
Dec 29, 2003
Messages
8,200
Re: 3.0 mercruiser losing rpm's after warming up

Sounds like something is tightening up, or you're starving for fuel. Check the lube in the outdrive. Make sure the water pump is working. Did you do anything with the filter in the carb? Define tune-up. That could mean anything from plugs and rotor to plugs & rotor, gearlube, oil & filter, and water pump. No two dealers I've worked for define "tune-up" the same way.
 
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bake415

Recruit
Joined
Jul 11, 2004
Messages
3
Re: 3.0 mercruiser losing rpm's after warming up

I had the plugs,wire,cap and rotor change. Outdrive lube level is fine, had it change before season started. The water temp shows between 130 and 140 after running for a while. I've not checked the fuel filter. I did notice that I can shut it down and restart it 10 to 15 minutes later and it runs fine again for a while.
 
Wotknot

Wotknot

Petty Officer 1st Class
Joined
Aug 6, 2002
Messages
310
Re: 3.0 mercruiser losing rpm's after warming up

possibly your coil
 
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akriverrat

Chief Petty Officer
Joined
Oct 31, 2002
Messages
588
Re: 3.0 mercruiser losing rpm's after warming up

plugged fuel tank vent? open cap after it starts bogging and listen for the sucking sound.
 
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AussomeA

Recruit
Joined
Apr 6, 2009
Messages
3
Re: 3.0 mercruiser losing rpm's after warming up

I'm used to car motors, but these should still apply..

What grade fuel are you running? If you haven't been running premium try it next time you're out.

You might possibly need to adjust the timing.
 
F

fyrfightr

Petty Officer 3rd Class
Joined
Aug 13, 2007
Messages
93
Re: 3.0 mercruiser losing rpm's after warming up

man, I hope he figured this one out. This thread is almost 5 years ols ;)
 
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