Yamaha 115 bogging

[CrisCrosAplsos]

I have recently purchased a 2002 crest 3 pontoon boat with a Yamaha 115 four stroke. The boat was sitting over a year prior to purchase so before I didn't anything i completely drained all fuel and filled back with 100% has with some sea foam to help clean injectors (don't know what has it had it in before i had it). When i get it on the water the motor idles great and even runs perfectly up to 4200-4400 rpm. But anything after that it will run for about a mile then it bogs down for about 2 seconds then picks back up and will run another mile or so and do the same thing. I've ran it for 1.5 solid at 4200 rpm never bogging once but anything over 4400 and it doesn't like it. Any help would be greatly appreciated!