1983 50 hp mercury 30psi compression on all 4 cylinders

[mmarr]

At the end of last summer, engine was running fine as I was going across the lake running full speed and engine acted like it was running out of fuel so I stopped and switched tanks while engine was running. I pumped up new tank and took off again but after about 200 yards same thing happened. I rebuilt the carbs with the kits but didn't replace floats same thing....This spring i rebuilt fuel pump on top same thing...I took carbs off again rebuilt bottom fuel pump but when I put them back on , I only had idle speed at lake when under a load. I test my compression and I have 30psi on each cylinder......I squirt some oil in each and they all will go to 140ish...I know my rings are seized but what could have caused this?

 

[Silvertip]

Re: 1983 50 hp mercury 30psi compression on all 4 cylinders

Overheat, lack of oil, lean carburetion. Does the overtemp alarm work?

 

[Laddies]

Re: 1983 50 hp mercury 30psi compression on all 4 cylinders

Could be carbon or rust from sitting it would not hurt to pull the intake port covers and look, if it's not scored or looked burned try soaking it with Mercury Power Tune

 

[mmarr]

Re: 1983 50 hp mercury 30psi compression on all 4 cylinders

thanks for the replys guys.......I still feel like it is carburatation as well.......would that explain the 30 psi.....thats what has me puzzled.....no overheat alarm and no thermostat on my model from what I have read and researched.

 

[Laddies]

Re: 1983 50 hp mercury 30psi compression on all 4 cylinders

The only way carburetion would cause low compression is if you ran the engine in a lean condition till it burned the pistons, and then the chance of them all being equal in PSI is almost impossible. Have you checked the compression gauge?

 

[mmarr]

Re: 1983 50 hp mercury 30psi compression on all 4 cylinders

I squirted a little oil in each piston, the they all read 130-140psi.....bought compession gauge at Harbor frieght so it is a cheap one.

 

[Mi duckdown]

Re: 1983 50 hp mercury 30psi compression on all 4 cylinders

I puzzled. you were running 50:1 oil correct? .02

 

[oldman570]

Re: 1983 50 hp mercury 30psi compression on all 4 cylinders

Could be carbon or rust from sitting it would not hurt to pull the intake port covers and look, if it's not scored or looked burned try soaking it with Mercury Power Tune[/QUOTE

I would do as Laddies states as if the motor acted as you say it did last fall the chance of a overheat is very likely. Checking for any scouring and the condition of the rings will show if the motor was overheated. Using the Merc Power Tune will help decarb the pistons and rings and the compression may come back up. Any scouring is a sign that you may have more trouble in a short time. JMO
Oldman570

 

[mmarr]

Re: 1983 50 hp mercury 30psi compression on all 4 cylinders

Yes Mi duckdown.....was running 50.1.
I think I may take laddies and oldman's advice and pull the intake port covers and look......
Once again guys thanks for your advice !