I had the same sort of problem with my
bx2350 (for an entire year), it would start to sputter and lose power the rev up again, die down and rev up again. It was especially bad going up hills. It was ok when the whole tractor was cold but when it would warm up the trouble started.
I changed 6 sets of fuel filters and replaced the air filter. It had been bad enough last winter blowing snow but this summer summer it got so bad that it wouldn't even drive on flat ground and finally I had to use my old 1985 Honda Big Red to pull the tractor to the yard from the garden,about 100 meters.(that was SAD).
I called the dealers mechanic and he went through all of the usual BS about the Bx as in did I check the fuel filters (Doh) lift pump? well yes at $114.00, fuel tank for trash, and fuel cap (yes and yes), water in the fuel? (nope not after $48. worth of sea foam and other water dispersant's)plus I run clean fuel and have put on a sediment bowl before the first fuel filter and also have a filter and a sediment bowl on my bulk tank.
Then he says "yup sounds like you have a fuel delivery problem, this could be interesting".( and he's one of the bright ones)
Then he says that they have on occasion had a problem on Bx's with air bubbles getting caught in the fuel line between the first fuel filter and the tank which is right on top of the transmission. So when the transmission would warm up the trapped air bubble would expand and for the most part block off the fuel flow. Which would explain why it would run fine cold.
So what I did was disconnect the fuel line before the first filter and and then I blasted compressed air back into the tank.
PROBLEM SOLVED it hasn't missed a shot since, plus I have an extra lift pump and enough fuel filters for the next 5 years. (whata deal huh?)
Give it a try, air is cheaper than fuel filters.
David