2013 Merc 20hp 4 stroke - Low Compression??

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Elliomcmh

Seaman
Joined
Mar 22, 2011
Messages
65
Hi,
i have a 2013 Merc 20hp 4 stroke. I decided to check the compression after some vibration at trolling speed. I got 55-60psi on both cylinders, is this normal? I remember my old evinrude compression being significantly higher.

i checked the compression on a cold engine, throttle in the idle position, and had the spark plug in the cylinder I wasn’t checking, not sure if this is the correct procedure.

Thanks for the help!!
 
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Elliomcmh

Seaman
Joined
Mar 22, 2011
Messages
65
Ok I checked both cylinders with the throttle at 50% and 100%, I’m still getting 55-60psi on both cylinders. I also removed both plugs and tested each cylinder that way at 50% and 100% throttle, and it was still 55-60 psi. Engine was cold, 55 degrees outside.
 
R

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
37,964
Something is wrong with your gauge or you have serious engine issues !
 
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Elliomcmh

Seaman
Joined
Mar 22, 2011
Messages
65
it’s a new gauge I got off of amazon. I could try buying another gauge tomorrow. Would it idle fine with a little vibration at 1/4 throttle and run fine at top speed if the compression is this bad? It’s on a Tracker Grizzly 1448 and runs 22 mph with a 10p prop.
 
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E

Elliomcmh

Seaman
Joined
Mar 22, 2011
Messages
65
Update: I just tested the compression on my lawn mower, the spec is 160psi and the gauge was right at 160psi, so I guess the gauge is good???
 
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Elliomcmh

Seaman
Joined
Mar 22, 2011
Messages
65
I just did some research and it looks like some of the Tohatsu made mercury small outboards have an automatic compression release, I wonder if that is why it runs ok but has low compression.
 
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