Does the throttle linkage have a very stiff spring on it? Normally, the throttle return spring can be overcome by pulling on the choke knob. Is there a reason you don't want to hold the throttle open slightly while pulling on the choke cable? It shouldn't be necessary to do that, but it's pretty obvious there's something going on with the fast idle cam that's interfering with getting the choke applied. Even automatic choke carbs need a little throttle opening before starting to let things index properly.
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!
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