Z1OwnersClub GB

Hi, sorry to ask on the Z1 forum but struggling to find a solution.

I bought a solid running z650 B1, UK bike.

Filled with new pump fuel and after about 3 miles it just died on me. Thought it had sucked rust from the tank so removed and cleaned that as well as the carbs (including jets.)

Added new fuel. Previous owner had replaced spark plugs before selling it. Has new points.

I have a spark on all four cylinders. Fuel is getting into carbs (and plugs look wet after attempting to start). However it won't start.
Will run (briefly) with easy start spray into airbox (with filter removed.)

Any thoughts on what else to check?
Many thanks in advance.

Start procedure for all Z's.
Fuel on, let the bowls fill. Full choke. ABSOLUTELY ZERO throttle input, hit the go button, when it's starts it'll rev to about 2.5k, feather the choke closed until its revving at about 1500 rpm. After a couple of minutes either ridden or standing close the choke completely.
ANY throttle input whilst starting and you'll flood it.