I suffer from the same issue. Only stalls when in long queues. Remove air filter elbows and put fuel into carbs it boils immediately. Heat is all at top of engine/inlet manifold allowing the carbs to get too hot. I have yet to fit an electric pump to see if this help, but I am looking to find away to get the heat out of the top of the engine bay. This as far as I can see will stop the fuel boiling in the carbs. This has caught me out 3 times now the first time when it stopped when I was stuck in traffic bringing it home when I bought it the second waiting to get into Enfield Pageant and the third waiting in queue to get into Uxbridge show. This Is why I am trying to get hazard lights to work!!!