2000 xp midrange bog

i need some help with a 2000 xp with 951 engine. so far i have fixed the leaking exhaust, both at the manifold and cone. i have also rebuilt the carburaters. when i went to test it there was a bog right from the bottom, but it idled fine both in and out of water. well i later found that problemto be the accelerater pump nozzles in venturi were clogged. fixed that now jet ski idles great jumps out the hole like a rocket, and then it seems once the accelerater pumpcycle ends it bogs. it will only do this if i slowly accelerate, if i just nail it off the bottom it will reach full speed and runs great. if i let off on top end alittle and hit it it will respond good but if i let off to much it will bog. i am very certain the carbs are clean aswell asrest of fuel system. my low speeds are out 1 5\8 highs at 0. i tried turning highs out 1\4, but that didnt help it was to rich on top end, and kept flooding. it seems to me the problem is coming in at the beginning of high speed circuit. could it be the jetsize? this engine was rebuilt and supposedly it ran fine after until it sat for 1 1\2 years. i took head off to check gasket originally when i was diagnosing the water leaking into engine, but it was fine and i replaced it with a new one also i noticed a 50 stamped on top piston. is that a .050 over piston, and would that have any effect? any help greatly appreciated.