Re: 82 merc 9.8 factory psi
I do not know the factory specs new.
However, I can tell you my experience with 9.8's and 7.5's is as follows:
Relatively low hours 125psi
Most motors read 105 to 120 (These run just fine with good power)
Lots of hours 100 to 105
less than 100; really worn out or a problem somewhere.
This is from several motors, maybe 15 or so. And using mostly KD & Sun compression gauges which should be good. I think you are supposed to check the compression with the engine hot and at WOT which will require that you block out the start in gear protection lever.
More important is whether the two cylinders are fairly close together, say within 10 to 15 psi of each other.
Hope this helps.
