Hi,

I just got a 2006 Kawasaki STX12F ( Jet ski with a 1200 cc fuel injected engine.)


185 hours and a dead #3 cylinder. Dead as on zero compression. With the plug out cranking there is a whisker of pressure sucking and blowing, but there is either a hole in that piston or a missing valve? Surely there'd be some serious clanking if a valve dropped.

Also these are high compression engines and known for blowing through/cracking/wearing pistons.

Boroscope won't fit through the tiny plug hole, but got a view of piston top and it was... it was there, there is a top of the piston (at least within view of the spark plug hole)

Cam lobes looks pretty, no damage. Owner changed oil regularly, garage kept nice machine.

It starts and runs. Other cylinders check good on compression.

Didn't hear anything clanking, like a valve bouncing on top piston, overall fires right up and sounds good. But it dies, but starts back up. Feels a whisker bad gas, injector clog maybe, and service paper mentioned bad gas (cause of prob?)
-UPDATE-Pulled injector rail and they are bearely spraying, so will dig into fuel deeper tomorrow.

Silly question- can it be run as is? As a 750 cc? 🤔
With the #3 injector disconnected, no fuel would be present. If it has a hole in the piston, what would that compromise? 
Also on that note if a valve is open and i run it , wouldn't that allow other cylinder exhaust into that cylinder? Any way to figure out if piston or valves are bad without pulling head?

I don't need a fast jet ski. Something to toodle around at 10mph would be bitchen Camaro from my view.

Any guidance appreciated!

Waverunner with a dead cylinder