Compression

[rodsnguns]

Will a mid 70s 70hp Johnson still run decent with the compression on all 3 cylinders averaging 70 to 80 psi ?

 

[Mc Tool]

Will a mid 70s 70hp Johnson still run decent with the compression on all 3 cylinders averaging 70 to 80 psi ?

No .

 

[racerone]

you have a bad gauge, loose head bolts or a motor that needs a rebuild..

 

[racerone]

Time for a new 4 stroke?

 

[rodsnguns]

Ok, went and got a higher end compression tester to see if my obviously cheep one was junk. The original readings were all 3 between 70-80. The better guage shows top-115, mid-110, and bottom 120. I assume these numbers are acceptable for a 1977 year motor ?

 

[racerone]

in my opinion they are too low.---Should be 140 or more.

 

[Chris1956]

IMO the compression values are close enough to indicate the motor is good. I say run it.

 

[Crosbyman]

not so bad for a 50 year old engine...
if it works don't fix it.

maybe try some engine cleaner/decarb product to clean out some carbon deposits. Some like Seafoam some don't.. no harm in trying see utubes.

Evinrude engine cleaner or Merc power tune should flush out some nasty stuff.