90 HP Mercury Compression Readings

Hi All, I'm looking at possibly buying a 1991 Mercury 90HP (oil injected) long shaft with power tilt. The seller claims that a compression test has shown 120 PSI on all three cylinders and that no major work has ever been done on the motor since it was new, only seasonal fogging, annual gear case oil changes, new impellers, plugs etc. I would like to do my own compression test before making an offer and have a couple of questions that I would appreciate some help with.

1. is 120 PSI close to factory spec?
2. I have a compression gauge but would appreciate advice on how to do a test properly and obtain accurate results.
3. Are there any specific concerns that I should look out for on this particular model and year?

Thanks in advance for any advice that anyone can provide.

Hemi

Hello 120 PSI is good for that motor. To do a compression test put the tester in the hole and spin the starter until the needle stops moving you want the readings to all be within 10% of each other. You will probably want to pull all the spark plugs out and disconnect the lanyard to bypass the ignition and do not put oil in the cyl before the test. They are good powerful motors stators are probably there weak point.

Thanks to both flyingscott and kimcrwbr1 for your help. I'm going to look at the motor on Tuesday evening and this gives me a good start on checking it out.

Hemi