F2 carbs mate? I had a #$%* of a time with mine, it'd start first kick, but wouldn't idle on #4, so I (carefully) pulled the pilot jet out and guess what? It was blocked so bad I couldn't unblock it, so I had to replace it. Now it idles like a new bike, sweeet.
Ultrasonic cleaning might work (the bodies will come up like new) so try taking your carbs to a gun shop where they do their own reloading, they clean all their used cartridge cases in an ultrasonic cleaner, so I reckon for a few bucks they let you leave your carbs in there overnight? Cheers, Terry.