'77 Johnson 70 hp loss of power

T

tdmiller

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I have a 1977 Johnson 70 hp that has experienced power loss. I decided to check the plugs and discovered a light gray colored goo on the center cylinder's plug. I'm thinking that this could be either a head gasket issue or a cracked cylinder wall. Judging by the fact that it is only one cylinder with this issue, I'm leaning/hoping that it is the head gasket. Can anyone offer me some advice or confirmation that my assumptions are correct?
Regards
T
 
tashasdaddy

tashasdaddy

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Re: '77 Johnson 70 hp loss of power

i'd say it's time to pull the head and investigate. check compression first, for a reference. could also be an exhaust gasket.
 
T

tdmiller

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Re: '77 Johnson 70 hp loss of power

Thanks for the advice. I hadn't thought about performing a compression test but that should allow me, assuming the compression is acceptable, to eliminate a cracked cylinder?
Regards
T
 
T

tdmiller

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Re: '77 Johnson 70 hp loss of power

Manual is on it's way.. In the mean time, I checked the compression over the weekend and the cylinders checked out within 2 pounds of each other. The highest was 121 psi and the lowest 119. Would this indicate that the issue I am having is related to the exhaust gasket? Thanks for any advice you guys can give. I've had this boat for roughly a year and have yet to turn a wrench on the motor, so I'm pretty green when it comes to outboard motor maintenance/repair.
 
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