What have you done today with your Austin Seven

[Reckless Rat]

Are you sure the carb is operating correctly? Take the ram pipe off and check to see that the damper piston is rising correctly. If the damper and needle are not correctly centred then it can stick and not rise. You can rectify that by loosening the jet mounting and resetting it's relationship with the damper assembly. However, with a standard engine and a LC head I would think that there isn't enough induction vacuum to properly operate a 1 1/4" SU, and as has been said earlier the raised position relative to the tank may be creating some fuel starvation problems. You may need to pump feed it.

You could try removing the spring and see if that makes any difference. The earlier H1 SUs (1 1/8") didn't have a spring.