engine keeps dying on me

[maxwell.riddle]

so ill get to the lake and launch the boat, runs good in the beginning. but goin down the lake the engine starts sounding funny, like its missing. then it starts losing power. and eventually die on me. i let it sit, take off the cover and wiggle the spark plug wires. try to start it and it wont start. only way i get it to start is by putting it in neutral and revving up the engine while starting it at the same time. but when i pull back the throttle to put it in gear, it dies. i end up putting it in gear fast enough and giving it gas to get the boat moving. but barely moves. and if i give it too much throttle it would die. so im putting to the ramp to get it on the trailer and it all of a sudden slowly and gradually starts running right.

i dont know what it is. i took the boat to someone and they checked spark and compression and everything and they tuned up the carbs and timing and everything to factory specs. havent replaced anything like spark plugs or anything.so i dont know what it is and need some help. thanks.