i have a technical question for anyone who can help. Is 98 PSI per cylinder good for a 1998 Mercury 135HP. I am looking at this engine, but those numbers seem low. Thanks in advance.

As long as its even between cyl its good,,

even is good but, that seem's pretty low have a 80hp and they run 110's 115's for a 1989 modle being even just means they have worn the same, seeing the year i would deffentlt check with an outboard shop, seems way to low for me,forgot to ask 2 stroke or 4 check with a shop to be certain, doug

Also check if the numbers you got were with the engine warmed up or not, if it's not warmed up, your readings will be lower.

-N.

The engine should be hot, all sparkplugs removed and the throttle wide open, to get an accurate reading, it does seem a little low but if they are even within 10% of each other that is good. I have an older 80hp and it hits about 110psi. If I remember right you only need about 65psi to fire a cylinder, hope this helps.