89 seadoo wont turn over all the way?

[truck]

i just got it today. at first i thought it was froze up but the pistons move down alittle bit and back up a little bit. will not go down all the way? i removed the bottom plugs and nothing happend. has anyone had this happen?
the old owner said that he was out on the lake and it just bogged down and stopped, then he parked it for three years.
any help i would love.
its a 1989 sp 600cc.
thanks
Truck
:stupid:

 

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took the head off and the pistons won't go down all the way. the front goes down past the exaust the rear will not.