You've got one of each- - - - -too many carbutetors, or not ernough chokes. Splitting the air flow through two carbs will reduce the vacuum you can develop by closing only one choke plate. Normally, closing the choke allows the manifold vacuum created by cranking to pull gas through all the passages in the carburetor. If choking only one carb allows a cold engine to start, that carb is jetted WAAAYYYYY too rich.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!