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I have a 1983 3-cylinder 70hp Johnson that has not been running well. It does not idle well, hard to start, poor acceleration, etc.. Today I checked the compression and the three cylinders were 126psi(top), 125psi(middle), and 110psi(bottom).

I know the bottom cylinder compression is not good and should be within 5psi of the other two. My next step is to determine why the compression is low... head gasket, scored cylinder..

My question is: Does anyone know what the "ideal" compression for this motor should be? If the ideal compression is say 145psi, it is probably time for a complete rebuild or a new motor. I've got my eyes on a new 70hp Yamaha, but I can't manage it financially right now.

Thanks for the free advice!
 

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Hi ET. on an 83 I would mic the runout on the cylinders and if within eight to ten thousands difference I would just hone the walls and throw a new set of rings in it. Make sure that you put the rings in with the "TOP" side up. They have a slight wedge shape to them. They will be marked
Good luck

[ 06-09-2003, 09:01 AM: Message edited by: Seefood Man ]
 
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