Re: 95 640 tigershark
With even compression (170 sounds really too high to me--Inaccurate gauge??) I'd suspect a possible lack of spark on one cylinder resulting in a lot of unburned fuel/oil in the exhaust from the offending cylinder. Or, your oil injection system (if it has one) is fouling up and putting too much oil in the cylinder. I've got no experience with a tigershark ski, so hopefully you'll get some better guidance. I do think it's worth putting a spark checker and making sure you're getting good spark on all cylinders.
Good luck,
JBJ