Still trying to figure this one out. Does anyone have a diagram of how the carb (fuel delivery) works when cold? I've changed my mind a little about ruling out the choke. The reason I say a little is that the choke flap stays open whether the temp is cold or hot. There's gotta be something in the carb that is opening to dump all of that raw fuel into the throat with out closing the choke butterfly. OR, I may be out there a bit on this theory so here it goes: Could it not be a fuel delivery issue and maybe an ignition problem(only when cold) ? When cold, something is retarding the timming so much that it will not fire correctly???  I'm just reaching thats all.....