Compression on 77 Johnson 140hp

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sancheta

Cadet
Joined
Aug 8, 2002
Messages
7
I recently purchased a boat (pick up next week) that has a 77 Johnson 140hp outboard on it. The owner sold it to me for a steal as he was told it ran great by the last owner and in reality it doesn't. I am a good auto mechanic but am unsure of two stroke motors. He said that it will start and run for a while and die out, and will not get over 2000rpm. The compression is off I realize at 75-90 in 3 cyl. and 120 in the 4th. What could cause this large descrepency in compression??
 
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wilde1j

Vice Admiral
Joined
Apr 15, 2002
Messages
5,964
Re: Compression on 77 Johnson 140hp

Scored cylinder walls, head gasket, broken or stuck rings, warped head (usually from overheating or not torquing) etc.
 
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Hooty

Rear Admiral
Joined
Oct 2, 2001
Messages
4,496
Re: Compression on 77 Johnson 140hp

First thing I'd try iz de-carbon the thing, see if the rings will loosen up.<br /><br />c/6<br /><br />Hooty
 
S

sancheta

Cadet
Joined
Aug 8, 2002
Messages
7
Re: Compression on 77 Johnson 140hp

Can carbonization build up in just 3 cylinders and not affect the 4th? I was planning to take the motor apart and change all the gaskets and clean the carbs? Will this possibly restore some of the compression??
 
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wilde1j

Vice Admiral
Joined
Apr 15, 2002
Messages
5,964
Re: Compression on 77 Johnson 140hp

Try Hooty's suggestion before disassembly. You may get lucky.
 
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