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.

 

[Jeff J]

Deleted

 

[airshot]

How long has the motor been sitting ?

 

[rodsnguns]

How long has the motor been sitting ?

Not really sure but I am guessing between 1-3 years. Leaning more toward the 1.

 

[rodsnguns]

Not really sure but I am guessing between 1-3 years. Leaning more toward the 1.

There is still a faint fuel residue smell in the lines. Carbs were redone about a year ago.

 

[airshot]

Motors that have sat unused for long periods of time sometimes has the rings stick and causes low compression readings. Thus the reason for using the power tune and other additives. Once the motor is running, try another comp test....results could be different !

 

[rodsnguns]

Kinda what I am thinkin too. Once I get er runnin I will do the decarb process then dump a can of sea foam in the tank . Mite just bring the Ole motor back to it's youthful days.

 

[jimmbo]

I am one of those who has NO use for SeaFoam

You could get some Power Tune/Engine Cleaner/ CRC's GDI Intake Valve & Turbo Cleaner, remove the Spark Plugs. With the engine tilted up, spray some into each cylinder, let it sit a while, rotate the engine a 1/2 rev and repeat.

 

[airshot]

I am one that has had great success with SeaFoam....to each, his own, I guess.....

 

[Crosbyman]

seafoam sure cleared up my honda snowblower hick-ups (surging) !
I was going to swap in a new carb ( from amazon) but never had to after I ran seafoam . Been good now 2-3 years