[DBrouwer]

What is the exceptable compression range for a 1998 90hp Mercury Outboard?Also, this engine has 3 carbs, looking from the port side I noticed at the top of each carb is an adjustment screw. Next to this screw, there is a threaded hole but without a screw. I noticed that gas will come out of this hole if the fuel bulb is pumped tightly---is this some sort of vent/overflow or is a screw missing on all of the carbs?

[12Footer]

You have a stuck needle valve in the carb. This needle valve is pushed up by the float,to shut off the fuel flow when the bowl is full. The carb must be removed,dssassemble at the float,needle removed and cleaned (or replaced if bad),and the carb re-assembled. Use a carb rebuild kit,and avoid re-using any of the gaskets.The compression is not in the Clymer manual.Try calling any Merc shop for that spec, or at least look for equal compression on all cylinders. The ones I have tested allways seeed low. Some of them had as low as 70PSI, but were equal, and the engines seemed to run fine at all speeds.But a shop will have the merc factory manual, and it is listed in them.