Most likely high speed jets plugged up. Here is a inexpensive tip to try first. Find or borrow if you don’t have one a portable gas tank that will hook up. About 3 gallons of gas and halt a can of seafoam. Mix that good with motor on muffs crank and let run about 15 minutes at idle. Shut off let sit overnight. Next day do same thing. Do this 3-4 hours with about 6-8 hour rest period for that stuff to work in carbs. Then take to lake and you can leave it hooked to trailer. Just back in enough to run motor in gear. Just put in gear and gas it up and let it run for a bit under load. Then launch and run the stew out of it. That should clean it out pretty good and loosen up any carbon on rings and some in exhaust. If that didn’t improve it then you start deeper trouble shooting. I bet this used boat has been sitting up a lot with old gas.
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