I bought this engine last summer to put on a 18 ft aluminum boat. Last week I started getting it ready for the water and noticed writing next to the spark plugs. The previous mechanic had written the compression numbers next to each plug. Each cylinder is labeled #80, #80, #80, and #80. I remember the mechanic telling me that the important thing to note is that the compression numbers are equal (or close) on all cylinders. The motor runs great, just a little light blue smoke coming out of the exhaust, it never hesitates to start, unless I flood it pumping the ball, and seems to run all day. I use it the boat in Cook Inlet to get from the village where I teach, to Homer a trip of about 24 miles. I just installed a tach last week so I could know how hard I was running the engine. Last year I rarely if ever ran the motor over 3/4 throttle because I did not know how much the motor could take, better to go slow 13kts or so and make it home than to try and set a water speed record and be set adrift waiting for a tow. I guess my question is I have a compression tool to test compression myself, is it as simple as taking the plugs out and cranking the engine, I read somewhere that I needed to ground the spark plug wires but not sure if I understand the "why" of that. And should I check compression after letting the engine warm up or do it cold? Also is #80 really bad if it seems to run just fine. Any help is greatly appreciated.