Hi Ed! Good to hear that you got'er figured out! When I dropped my mains, I also dropped the main jet tubes (main jet holder) and was looking for the collars to come out. They didn't and I didn't want them too either.
. It would have to be the only thing we didn't consider! At least it was indeed a carb specific problem thus only effecting the left carb.
Like Phil said, I too dropped an idle mixture screw to only find myself going blind trying to find that teeny metal washer! Seems like all the tiny parts get lost on the left side of the motor...
Did you or did the dealer ever find the original collar that was not re-installed? Or did the dealer have one in stock?
Pictures from
A Carburetor Primer 
