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If the engine revs ok but there is no thrust from the pump then you need to inspect the propulsion system. Likely causes are something in the intake side of the pump ie ski rope wound up on the driveshaft or trash over the intake grate, damage to the impeller from injesting rocks or worn out bearings in the pump and excessive clearance between the impeller and pump housing.
It is mostly a visual inspection to look for an obvious problem. If you do not know what you are looking for then a shop could do the inspection and estimate for about ! hour labor. Repair cost would depend on what problems were found.
If the engine revs to max rpm then that is not the problem.
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