Isn't the cold starting arrangement on DCOE Webers a separate, crude fuel-air mixing passage that is a separate, parallel source of air and fuel that bypasses the the source and system that the throttles control? And that the throttled main bores have no enrichment provision for cold-running?

If so, opening the throttles to get power from the engine has the effect of diluting the rich mixture from the cold starting provisions with non-enriched mixture from the idle and main system. Lots of throttle opening would result in minimal enrichment from the combined systems. Icy cold ambient air entering the main barrels would make for lean behavior.

I had a Solex downdraft-equipped '64 Alfa with such a starting device, and it would start and run at fast idle while cold, using its "choke" device, but not give any well-behaved power until the manifold and under-hood air supply had warmed up.

Charles Greenlaw, Sacramento