Electric choke problem.

Hello, I have a strange problem with my XK120 FHC, that I cannot cure. It has a 3.4 engine, 9/1 Pistons, D type cams, 2" HD8 carburettors with UO needles, 123 Ignition system, set at 10 BTDC and 36 at 3,000. When car is hot it runs ok and gives 204bhp on Dyno. There is an electric choke with a manual switch rather than thermostatically connected. The problem I have is that starting from cold, with the choke on it will not run at 1,000 rpm unless I push the needle down with my finger, then the engine goes up to 1,000 rpm, I take my finger away, but the revs slowly reduces after a short time which lets the needle go up, so it then starts to flood its self then it stops. I have tried the nut on the top in several positions and it is currently about one full turn from the bottom. What I can tell you is that with the engine hot, if I put the choke on and flick the throttle open, it all seems to work correctly I.e. 700 rpm Idle without and about 1,000 - 1,200 with it on.
The main jets on the HD8 are set about 1/16 or a bit more down and I have set the jets for the highest rpm by going up and down then adjusting the volume screw.

I tried squirting carb cleaner around spindles and can't see any suck in leaks.

Any thoughts from the experts, appart from take it off and put a manual choke like an E type !!

thanks very much from England

regards
John