Compression fairly even but low

[hauntedbywaters]

Hi:
Great site!

'94 Mariner 60hp has fairly even compression (within 4psi), but all compression readings under 110.
Idles good, cosmetically looks great, but these numbers seem low to me from what I have read. (Why could they
not have been all 140, eh?). Anyway, are they definitely too low for this motor, or ??????

Thanks

 

[wired247]

Re: Compression fairly even but low

Those are good compression numbers for that motor. Relax. Have a beer.

 

[hauntedbywaters]

Re: Compression fairly even but low

Kewl - guess I will have to put on my negotiating hat...

Thanks ...

 

[1FASTLASER]

Re: Compression fairly even but low

Whatcha think wired..... A prime candidate for a good Decarb and them numbers prolly will come on up

 

[wired247]

Re: Compression fairly even but low

Maybe not. Most modern fishing motors are low compression motors. I had a 3.0 liter 225 that was 110 lbs from Mercury.

 

[Texasmark]

Re: Compression fairly even but low

I have a '02 90 and the manual states that any reading under 120 COULD be a reason for alarm. My current compression numbers are nearly even at around 110, engine runs 57-5800 right at 50mph on a cool day...see Avatar.

However, I'll second the motion on de-carb. I learned of it on this site years ago and I decarb (more or less) every engine on my place and I have a couple dozen of the different types/applications, only one marine. Sea Foam and the use thereof has made a significant impact on all my engines and I keep half dozen bottles on the shelf at all times. Works for me!

Mark

 

[Dukedog]

Re: Compression fairly even but low

Tha MAIN thing when reading comp is tha gauge itself if lookin' for good numbers. It has ta be a "known" accurate gauge. Not just new! ie: HF gauges might read 160 or 110. Ya never know with any of 'em............jmo.

 

[Gerry3]

Re: Compression fairly even but low

That is food for thought, my 1994 30hp shows 170psi on both cylinders lol.

 

[hauntedbywaters]

Re: Compression fairly even but low

I went again to look at the motor. Checked compression (cold) and got the same numbers. We warmed 'er up and set the throttle high. Got low 130's on all cyls. using the same gauge (the owner's). wtf ???
But, ending up not 'pulling the trigger' for other reasons.

Anyway, thanks for the responses and info.
(As my wife said, there are other motors in the sea. )

 

[wired247]

Re: Compression fairly even but low

Compression numbers should ALWAYS be taken at operating temp with an open throttle.

 

[hauntedbywaters]

Re: Compression fairly even but low

I have heard that from several sources and my results seem to support that.

Thanks ...