Hi Guys,

Hope someone can help here.

TB42 Carby, running fuel only. Has new plugs, coil, leads, extended rotor button, points.

Choke is functioning normally, fully closed on a cold start and gradually opens to fully open when warm.
I can't see any obvious vacuum leaks.

Basically it'll always fire up first go, idling rough and accelerating like it's running on 4 or 5 cylinders, backfires under a bit more load or if it's been idling for a while and i try giving it a quick stab.
Idle speed is all over the place. Give it a rev and it'll be up around 1100rpm, just breathe on the pedal and release and it'll drop down to 450-500rpm.

Once warm it hardly misses a beat, runs incredibly well at idle and pulls well right through the rev range. Even towing hasn't been a problem. But until it's warm, it runs like a bucket of shit!? Tonight I didn't even drive it, just at idle in the driveway while watching the choke butterfly slowly open and it was backfiring regularly while giving it a quick rev. Also concrete is black from crap out the exhaust - this never used to happen...

Any ideas really appreciated!

cheers
Mark