between 90-120
185psi
The spark plugs on a 1988 model, 70hp Johnson outboard, should be gapped to .030in.
I should be equal on all cylenders and about 110 to 120
125 is the least
In the early 1970's, when you could still get good gasoline, outboard compression in the 180-190 psi range was common. If your 65 hp Johnson is running in the 100-150 psi range, this would be acceptable, and the engine should still perform well on todays fuel. The important thing to note with compression readings however, is that the difference between the highest and lowest reading, is no more than 15 psi. One more note, avoid fuels containing alcohol if at all possible.l
I have a 2005 and compression should be close to 120 psi. Normally a good engine will have compression between 115 and 130 psi but a leak down test should be performed also to know the full condition of a cylinder.
should be at least 100 PSI and the difference between cylinders should be less than 10% of each
120 psi
should be able to find it at this site http://www.marineengine.com/manuals/johnson/index.html?gclid=CKXf-92Xg5QCFRZjnAodnjN_WA
Should be a 71 year model
optimally at least 100 psi on each cylinder, but the most important thing is that both cylinders are 5% within each other.
A 7.5 hp outboard will need around 90 - 100 psi of compression to start up and run. Anything over this pressure is a bonus. Also, you want there to be no more than 10 - 15 psi difference between cylinders.