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1979 1/2 Mercury 115hp inline 6 low compression

U

uskr005

New member
My boat and motor have been in my family since day 1. It has lived most of its life in northern MN approx 900ft of elevation. In 2008 I moved to WY and brought the boat with me approx 5000ft of elevation. I ran it with the low elevation jets for several years. This spring I rejeted trying to get the performance I had in MN. After rejeting it doesn't seem to do any better. I did a compression test and found 68 - 70 psi on all 6.

The motor is on a 78 lund aluminum. The motor is proped with a 14X17P, max rpm 4500. In MN rpms would run 6000 or higher with the 17P prop used it for waterskiing. Most of the time ran a 19P prop. I am still able to pull my wife up on a wakeboard, but there is no chance of pulling myself up.

Did I mess it up by running the wrong jets?
What should the compression be?
Whats is wrong, I'm guessing my rings are gone.
How hard is it to fix?
Where can I find a better manual than the seloc I have?

Any help would be appreciated.
 
I did a compression test and found 68 - 70 psi on all 6.
Click to expand...
The engine is 34 yrs old and tired. The good thing is all cylinders are equal. Was it done w/all plugs out, kill switch activated on a warm engine? If you had a hard time breathing at that elevation so does the engine.
 
all plugs out.
key off jumped starter solenoid to crank.
ran on the muffs prior to checking compression it doesn't have a temp gauge.
 
Are you sure that all cylinders are firing? I would test the spark output using a test board that can show all 6 spark wire outputs simultaneously for comparison...loud blue snapping spark. Buy, borrow or make one.
 
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