1960 Johnson 10 HP Compression Question

[dhughes214]

Just tested the compression on my Johnson 10 HP and I'm getting 65 and 70. Sounds low to me, but I can't find compression anywhere in the manual so not sure what it should be.

 

[Daviet]

Re: 1960 Johnson 10 HP Compression Question

I don't think you will find any compression specs listed. If you are using a recoil starter, 60 to 70 lbs, within 10% of each other is ok.
You might decarb the engine and see if you pickup more compression.

 

[dhughes214]

Re: 1960 Johnson 10 HP Compression Question

How exactly do you decarb the engine?? I can't get it to start, and I've replaced EVERYTHING I can possibly replace. So I was thinking maybe it was compression.

 

[Fuzzytbay]

Re: 1960 Johnson 10 HP Compression Question

What exactly did you replace? Do you have spark? Did you rebuild the carbs?
Compression numbers a vauge, as long as they are close, ie within 10lbs should be good.

 

[wbeaton]

Re: 1960 Johnson 10 HP Compression Question

OMC didn't publish compression numbers. 65-70 psi is low. Most I see are in the 80's. I've never seen one over 90 psi. I've seen them run in the 70's, but lack power.

Start at the beginning. Spark + fuel + compression. Compression is marginal at best, but it should at least pop. Do you have spark or fuel?

 

[tx1961whaler]

Re: 1960 Johnson 10 HP Compression Question

Your compression is OK.
Check for spark with a spark tester; both cylinders should jump at least a 3/8" gap with a healthy blue/white pop.
Once you have verified that there is spark to both cylinders, than all that is left is the fuel system.

Once you get it running, if you don't know how old the water pump impeller is it needs to be changed. It's rubber and breaks down over time.

All of the tune-up parts are available here at iboats.com.