1990 90 HP merucry

[Chundris]

I just recently bought a second hand motor for my 18' speedboat it seems to have compression issues; the middle cylinder is reading lower values the the other two; any idea what the problem might be?
Is this a common issue?

[boats.net]

If the compression is low the engine needs to be rebuilt, you wont know what caused it until it taken apart and inspected.