BX2350 Runs fine for a hours then runs rough

[Atkinsra]

I have a BX 2350 that runs fine for about a hour thens starts running rough when it's under a load (mowing or incline) I have drained the fuel tank and replaced the fuel filters twice. Also has a new air filter. I used the tractor Friday discing a small parcel of land, it started acting up so I shifted it to low gear and it seemed to run ok. Anyone have any ideas?

 

[BXinNH]

Clogged fuel tank vent? Try loosening the fuel cap when it starts running poorly. Could something be settling over the fuel outlet in the tank and then drifting off? Good luck.
Matt.

 

[Leejohn]

Fuel filter, pump, or bad line.