2007 30 HP mercury compression?

jayman02

Recruit
Joined
Apr 20, 2012
Messages
1
I saw a 2007 30 hp mercury 4-stroke outboard for sale, in the description it says all 3 cylinders compression read 70 psi. I contacted the seller and they told me that there is no spec PSI range listed by them manufacturer, only that the cylinders be within 15 % of each other. I have searched everywhere for more information but I cannot determine if this is an acceptable compression. Does 70 PSI on all 3 cylinders indicate a good running outboard? I appreciate any insight. Thanks.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: 2007 30 HP mercury compression?

From the Service manual:
COMPRESSION RATIO:
Compression Ratio 9.7:1
Cylinder Compression*
(Electric Models Only, Cold Engine @ W.O.T.) 180 - 210 psi (Peak)
His gauge must be way off or it wasn't tested....
 

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: 2007 30 HP mercury compression?

Different quality of gauges will often vary greatly.

If you are seriously thinking of buying the motor buy or borrow a decent guage from NAPA or AutoZone and test the motor yourself, also test to ensure a hot blue spark of at least 7/16 inch, and most importantly, take to boat/motor out for a ride on the water so you can KNOW that it performs well. Running on the hose, or buying a motor based on compression alone is no warranty that the ignition or fuel system work.
 
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