AndyM, have you considered removing, cleaning out, and sealing your fuel tank? It is most probably quite rusty inside like the tank in my '80 RQB-3109. The rust in the tank flakes off and travels through your fuel lines and will clog even a new fuel filter. It's really not all that hard to remove the tank and the sealant should protect your tank for another lifetime. Watch the many youtube videos on how to remove the rust. The POR15 kit is $73 on Amazon.
Rust clogging a brand new fuel filter can easily mislead you into thinking that your new carb is suddenly having problems again. As was