- Good compression for that model is 130 - 140 psi.
- Where to start? 0 compression could be valves, head gasket, or internal engine. Regardless of which, you are going to have to start by removing the cylinder head. So- remove the lower cowlings, flywheel, timing belt, and valve cover, then pull the head. And yep, you should have a manual. If you have a little experience working on outboards, a SELOC manual should work, however if you are a greenhorn, I would suggest factory service manual from Merc, It's a bit more comprehensive.