What should the compression be on my '72 Johnson 100hp?

[oldrudedude]

What should the compression be on a '72 johnson 100hp and why can't I find it in the factory manual?

 

[tashasdaddy]

Re: What should the compression be on my '72 Johnson 100hp?

not published, due to the fact that guages read differently, and methods vary. preferably, 100psi or better, but the main thing is that the reading are within 10 % of each other. read about it here http://forums.iboats.com/showthread.php?t=299680

 

[oldrudedude]

Re: What should the compression be on my '72 Johnson 100hp?

Thanks for the response. My Equus gauge does not have marks between the fives, so it is hard to get a detailed reading with it. Testing consistantly showed 125, 125, 121, 125. I assume it is alright but am curious as to the cause of the drop in #3. This motor is a replacement motor for my Johnson 140 winter project. I got it for free and don't know its history. I have had it running on muffs but never in the water. I have changed out the C fluid in the LU, cleaned carbs, timed and, link/synched. I would like to be sure it is all OK before it goes on the boat. Should I pull the heads and decarb or should I Sea Foam it?

 

[DGartzos]

Re: What should the compression be on my '72 Johnson 100hp?

You've absolutely, not at all, for-never an issue with the 121psi cylinder !!!
In fact, it is more a surprising coincidence that you've straights 125s on all other cylinders giving the age of your motor.

Sea foam it, if you feel it needs it, as you do not know it's history ...

- do not grow where not planted !!!

 

[Daviet]

Re: What should the compression be on my '72 Johnson 100hp?

I don't think there is any problem with those compression numbers.