I am just going to toss something out there, because your symptoms sound a little like what mine were.

I had a nearly brand new fuel filter on (mech fuel pump, 3/8 barb metal-housing filter), so I didn't think that was my problem. But for kicks, I took it off and I discovered that all I had left was the outer housing and a metal inner part, all of the paper filter part was gone, and the residue or whatever presumably in my carb. I didn't find any big pieces. I am pretty sure the filter was not like that when I put it on, or I would have heard it rattling.

Anyway, I disassembled the carb, blew out all the passages the best I could with carb cleaner and compressed air, and it seems to be fine now.

Greg