I agree that proper air screws first / fuel meter screws second is the proper way to do a VM carb adjustment. However, when the slide starts to open with a bit of throttle the pilot circuit quickly gets swamped. When I've been lazy and just twiddled the airscrew to get a decent slow run I've always found it ok.
Effectively the airscrew and fuel meter work in series with each other (though it's not a proportionate relationship) and they affect each other. You can keep your mixture the same by winding one in and the other out. What you do achieve by doing air screws first / fuel meter screws second is a truer carb balance. eg if you've got one airscrew out 1 turn and another out 2 turns to get the best mixture and then you do a balance you have to drop one slide slightly lower to compensate so your carb balance won't be spot on when you open the throttle, though you probably won't notice it. I'm also not so sure that Mikuni machining tolerances were close enough for it to have any significant effect.
Having said that, I do prefer to do things properly and 'play safe'
Effectively the airscrew and fuel meter work in series with each other (though it's not a proportionate relationship) and they affect each other. You can keep your mixture the same by winding one in and the other out. What you do achieve by doing air screws first / fuel meter screws second is a truer carb balance. eg if you've got one airscrew out 1 turn and another out 2 turns to get the best mixture and then you do a balance you have to drop one slide slightly lower to compensate so your carb balance won't be spot on when you open the throttle, though you probably won't notice it. I'm also not so sure that Mikuni machining tolerances were close enough for it to have any significant effect.
Having said that, I do prefer to do things properly and 'play safe'