5.7 merc running rough after warm up

[CatriderF7]

Hey i took my boat out for the first time yesterday and it started up easy, idles smooth. I let it warm up for a good 5 minutes to be safe, and it seemed to be fine, then we got out and it drove fine for a good 5-10 min at full throttle and then slowing down a slow cruise at about 1/4 throttle it would rev up and down by like 300rpm, and then if i tried to get into the throttle any more then that it started bogging like it was going to die. If i put it in neutral it runs smooth again. I tried new plugs, cleaned the contacts on the distributor cap/rotor. filled it up with $60 worth of premium and a bottle of seafoam (boat has been sitting for a solid year before i got it)

anyone know what would cause this? carb issue? its weird because it runs fine at first. and the temp guage gets up to right where its supposed to be and never really gets higher.

 

[CatriderF7]

Re: 5.7 merc running rough after warm up

Well i got it fixed. But for anyone else with this issue, I Pulled the carb apart and it was clearly never taken apart (judging by the paint on the bolt heads not being scratched or chipped) and the whole thing was surprisingly clean, besides some dirt in the bottom of the bowl. but I cleaned that out and sprayed it out good with carburator cleaner and put it back on, and it ran great.