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Old 06-14-2010, 01:12 PM
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Default 70 hp 1977 Johnson

I have completed a compression check on my 1977 70 hp Johnson. Can some one tell what psi is good and what psi is not ok?
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Old 06-14-2010, 02:52 PM
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Cylinders should be even, no more than 15 psi difference in compression readings between cylinders.
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Old 06-14-2010, 09:38 PM
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Quote:
Originally Posted by boats.net View Post
Cylinders should be even, no more than 15 psi difference in compression readings between cylinders.
Thank you for that answer and i had read that in the manal. I am reading 93 psi on two cyclinders and 101 psi on the other. This motor is stalling out when i put it in gear. Is it due to the fact that two cyclinders are under 100 psi?
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Old 06-19-2010, 12:26 AM
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No its not stalling out from compression. You may want to check your shifter cable as it comes into the motor, adjustment thumbwheel you can adjust. It may be a linkage issue. This problem most likely can be worked out pretty easily
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Old 06-19-2010, 03:11 PM
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I replaced the power head with a differents parts motor i had and it had more compression. This allowed me to but it in gear without stalling the motor. A new problem has risen however. Upon acceleration, it has a dead spot half way through. If i push it on through it will go on, if i hold it there it will kill the motor. Also, at full throttle it slows down when i turn the motor sharply. This issue is not in the cable.
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Old 06-21-2010, 10:02 PM
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the compression readings are within 7% of each other. That is ok. its not stalling due to compression, something else is causing that. Have you re-built the carbs recently? How old is your gas? It may be a carb issue
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