1978 Johnson 75hp compression

[daleyeah]

Just traded for a boat, with 1978 Johnson 75hp. Checked compression all 3 cylinders have 80psi. boat will run in cooler temps once it gets up in the hot part of day it bogs down at 3000rpm and will not plane. Is 80psi the problem?

 

[racerone]

Should be reading about 140 PSI.----So step #1 is a test with another gauge.

 

[daleyeah]

Should be reading about 140 PSI.----So step #1 is a test with another gauge.

Gauge is brand new. It is the Harbor Freight one tho

 

[racerone]

Test with another gauge.----Or if gauge is good you have serious piston / ring problems.

 

[daleyeah]

Test with another gauge.----Or if gauge is good you have serious piston / ring problems

Test with another gauge.----Or if gauge is good you have serious piston / ring problems.

Also I've read after compression check, to spray wd40 in cylinders and test again. Is that something, I should also do?

 

[F_R]

Also I've read after compression check, to spray wd40 in cylinders and test again. Is that something, I should also do?

Squirting any kind of oil into the cylinders is cheating. Hiding the truth

 

[daleyeah]

Squirting any kind of oil into the cylinders is cheating. Hiding the truth

I'll return gauge and get a loaner from auto parts store.

I did as the manual said and tested on muffs. People locally have said I didn't have to check compression on a hose. This true?

 

[daleyeah]

Re checked compression on 2 more testers. 120 on all 3 cylinders.

During the compression check I noticed the cam yoke on the throttle rod was upside down.
Would this explain why I have a stumble or bog when going into WOT?
Also carbs are clean previous owner rebuilt them, replaced power pack, coils and stator guessing at the issue.