On a 2 cyl 650 jet ski if you burn the head and machine some of the
surface will it run like **** in the water but run great on the bench?

 

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How much did you mill off the heads and what thickness of head gasket? What are your squish numbers, compression tests? Not sure how you would test and adjust on a bench unless you have a water dyno or something. Let us know I am curious on a bench test for a jet ski.

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