Re: How to check compression on 9.8hp
It's easy. Take out both plugs. Put spark plug wires somewhere they won't spark to the engine or other ground. Put screw in type compression tester in one cylinder. Turn throttle to full open (gear will have to be in F or R). Pull cord until compression reading stops rising. Do the same for the other side. It will take 3+ pulls. I just pull 5 or 6 times. One important thing is to do the same test on both sides - so if you pull a certain number of times instead of just pulling until it stops rising, make sure you do it the same number of times for both cylinders. I've tested two older Merc 110 (9.8 hp) a 67 and a 74 and they both had compression around 120 or 125 for what it's worth. Of course, it's most important they be around +/- 15% of each other.
