This thread is very interesting to me, as I am new to the jet ski thing, as where I just bought a used 93 GTX with the 587 engine & dual carbs. Mine is doing the very same things that your jet ski is doing. I did check compression on both cylinders before buying and there were 150 psi, and found cable going to injection pump fell off, and put back on. But after taking to lake and running 4 gallons of gas thru it, it will run on land, but dies in the water. checked compression again back home and PTO cylinder still has 150psi, but MAG cylinder down to ~90 psi (put several drops of seedoo oil in and it raised to ~120psi, still not good enough), so started tearing down, found several things wrong; 1) bolt missing on lower side of exaust manifold where bolts to side of engine,
2) bolt missing on lower side of rotary valve plate where bolts to engine and also o-ring missing against rotary valve, 3) pulled cover off mag/flywheel housing and there is oil at the bottom, assuming seal is leaking behind flywheel, and 4) (worst of all, the MAG side piston has the top edge is eat up and part of top piston ring is missing. My question is all this thing contributing to not running in "the water". I want to repair or replace these things to get it back running, the biggest being replacing the piston & rings with an oversized piston. From what I can tell, the internals (crank and all appears to be ok, but not sure how much play should be on the "rod". I"m mechanically inclined, and along with information, pretty sure I can get it back running, just how much $$ will it take. Any advise i would appreciate.
thanks,
Randy