Hi,
which Mikuni is it ?
Single or 2 carbs ?
Jet-sizes ?
Needle-settings ?
The Mikuni carbs wether they are flat or roundslide aren`t that easy to comprehend (at least not to me

)
As far as I am concerned the choke doens`t limit the air-intake it opens another fueljet.
This way Mikuni`s enrichen the mixture.
If you open up the throttle while starting...the choke will NOT work !
Once you take the float-bowl off you might see a small pipe sticking outta the bowl.
This is the passage for the fuel to the choke.
An air-compressor is doing a good job on this tiny pipe (usually I never use an air-compressor
at a carb but here there is no other way)
BTW: I trust that you`ve checked the ignition already lol
ray