1977 johnson 85hp compression reading good or bad?

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nate78

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Apr 29, 2012
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I have been having problems with my engine a friend said maybe i lost a cylinder to check the compression so I did the reading are 95-95-90-90. Are these good or bad?
 
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emdsapmgr

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Re: 1977 johnson 85hp compression reading good or bad?

The normal reading for compression on this engine when shipped from the factory was around 125 lbs per cyl. You may want to retest the compression with another gauge to verify the numbers. While considered low, it should run with those numbers, but probably won't make the hp it did when new. You could try to do a decarb on the engine and see if the numbers come up any.
 
JB

JB

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45,907
Re: 1977 johnson 85hp compression reading good or bad?

Hi, Nate.

Welcome to iboats. :)

Those numbers are acceptable. Conditions, gauges and methods vary too much to set some psi number as minimum.

Look in the Engine FAQs Forum for a good method. If you do it that way, with a good gauge, you might get higher numbers, but I would accept what you got the first time.

Good luck. :)
 
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nate78

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Re: 1977 johnson 85hp compression reading good or bad?

I bought new spark plugs and some sea foam ill try that and see if it helps any. Engine goes from having power to none then it will eventually open up again. Think it could be the plugs or ????
 
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emdsapmgr

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Messages
11,551
Re: 1977 johnson 85hp compression reading good or bad?

If the engine's power varies when you are running it-possible weak fuel pump. It may not supply enough fuel to keep the engine running at WOT. Try constantly priming the fuel hose bulb. If it runs fine when you constantly prime the bulb-it's a fuel delivery issue.
 
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