Glad you found it.
Not quite sure how air gets in since fuel is under gravity feed and wants to get out! Possible rubberised junk in the pipes or swollen inside?
I had to uprate the fuel lines on my old 250 RD. 220 main jets, Micron MKI expansion chambers and various reed, port, head and case mods plus 30:1 petroil meant fuel consumption was a bit heavy with the rev counter clockwise past the high beam lamp. Lack of fuel on those meant either instant skirt or ring seize near the exhaust port or melting of the plug earth bar and subsequent arcing to the piston crown. The bottom ends were pretty tough and the piston usually destroyed itself in a way that didn't score the barrel or disperse aluminium into the main bearings. i never had the exhaust side of the piston go soft, usually something much more spectacular.
Lifting the front wheel at 40 with the cheery wave of an L plate as you took MGs, Jags, CX500s and CB750s off the island was always fun. Well not so much fun with a CX500.
Memory kicks in that I had to split the fuel pipe to the two carbs just under the tank or something, with bigger pipes and bored out fittings. Suzuki reed blocks and RD400 carbs also now remembering. They had a series in Motorcycle Mechanics or Superbike about how to tune your RD. I was well in front of the curve with that. Been there, blown it up twice already. Still using Yamaha reed blocks? How quaint.