1997 Johnson 15hp Bogging Down Under Load w/Cowling On

Need some help please: Got a 1997 Johnson 15hp that's ran great and gets serviced every winter. Jut recently took it out after having carbs cleaned, fuel lines/spark plugs replaced, l/u oil, and prop rehub. The boat idles great and starts after 2 pulls, but after going full throttle for about a mile it started to slowly bog down. It never died. Took the cowling off for quick inspection, but didn't see anything. Put cowling back on and same problem. Decided to leave cowling off and just run as long as I could to see if that made a difference. Never had a problem when the cowling off, but as soon as I put it back on the problem reoccurred.

Thanks for the help!

Adam

Things to check................
Exhaust leak to the under cowling area. Most likely up through the shift rod tube
You missed replacing the high speed nozzle gasket when you cleaned the "carbs"...hint, there's only one. :mrgreen:
Loose or over-sized high speed jet.

Or exhaust manifold gasket leaking so your carb is sucking fumes. Happened to me with my 77 Johnson 15 hp.