Sudden increase in idle speed - Strombergs

[661]

I got stuck in traffic on the way to the Revival, got very hot and with a dodgy battery the only way to keep it charged was to hold the revs at about 1500. ( More heat!!)
Anyhow, back on the open road the idle had stuck at about 1100-1200 revs after the jams. Having got it back home the idle is still high, the idle screws are all the way unwound, the fast idle screw is not in play, all the cams are back to their stops, the dash pots are down. Has something odd melted/broken like the thermostat compensator, that mythical device that I know nothing of?

[661]

I've just found the vacuum T piece is split and the headlights don't rise. Would a loss of vacuum to the front carb allow the revs to rise?

[Chancer]

Absolutely, my first thought was an inlet manifold air leak, sorry that I didnt have time to post.

99.99% sure that is your problem.