Backfire issue when choke is pushed back

[Kingkitesurf]

Hi experts,
I have a 4.2 rebuild engine with 2 strombergs and 123ignition. When I start the car cold it needs full choke and does not run on all cylinders. After slowly driving for a minute or so slowly all cylinders start running. Then after a few minutes more and pushing the choke back the engine backfires a few times and then runs like a charm.
What could this be.
Carbs have been rebuild and I suspect the ignition has to do with it. Changed the rotorcap once and did not do the backfiring for a month. Then it got back.

[johnetype]

Yes, check the ignition timing but it sounds like only one choke is working. I'd check that both cables inside the choke Bowden cable are connected and operating the choke quadrants on the carbs correctly.