What size main chokes (not the cold start device, Weber refers to the restrictor that determines the smallest diameter of the throat a choke, just as on a shotgun) do you have? they are marked in MM. We find that many of these carbs, especially on triple setups, have way too big a choke installed. Some pop and pink on initial accelleration, or just plain drop dead. The reason is that at low vacuum the velocity of the "signaling" air passing over the jet venturris drops and won't provide good atomization, and sometimes, fuel.
The thing to remember about Weber DCOEs is that, as on most all Webers, the idle circuit actually makes up not just not the idle fuel delivery, but half to two thirds of the rest of the running range. It occurs to me that your problem might just be during the transition from the idle jet circuit to the main circuit. My thought is that you may have too big an air corector jet, or too small a main jet. Or, it could be a somewhat plugged main circuit. As far as choke diameter goes, I wouldn't venture much bigger than around twenty eight MM. We had a TR6 here that wouldn't run worth a nickel until we installed TWENTY SIX MM chokes. At that point it idled smoothly, and ran like a missle. The more throats you use, the smaller the restriction must be to get an equivalent result in gas velocity. Just something to think on.
By the way, Haynes puts out a pretty darned good book on Webers, with theory, exploded views, tuning reccomendations, and overhaul procedures.
Another by the way. It seems to me that you have too much ignition timing for this engine. That's far more likely the cause of the pinking you hear on accelleration. Start with it at absolutely factory stock, then mess with the carburetters. Advance it only as far as not to pink AFTER the fuel problems are solved
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon