Welcome to my sarcastic way of helping and adding information. Try not to get too butthurt about it, its just the way I roll.
I only read a few pages back on this single carb saga but you guys are all over the place with your tuning info. For christ sake, how can you give advice if you dont even know whether he has a fuel mix or air mix screw? Too many changes at once....only jetting but no tuning...many assumptions. This is why it is so hard to fix things over the internet.
Believe it or not, your symptoms are not always soley cause by improper jetting.
Whats your compression?
Are your valves in spec? These valves on these motors get tight in a hurry.
Any exhaust obstructions?
The easiest way to tell whether you have an air mix screw or a fuel mix screw (any professional tech should know this) is to determine whether it is on the INLET side of the carb, where the AIR enters, or on the OUTLET side of the carb, where FUEL is mixed with air to make that scooter go. Some have both...OH MY!!
Checked for air leaks?
Carb bolted on too tight? These carbs have a tendency to run funny when that is the case because the carb body distorts.
You are not running the stock airbox, therefore regarding hiw the air moves, everything changes.
Are you positve that your air bleeds are clear?
Have you tried a different needle jet or jet needle? Foe the record, my feeble mind thinks this could be one of your issues. You may also have a bent jet needle. If you never try other needles (which is always a step in the jetting process) we will never know.
Tried different slides with different cutouts?
The suggestion that your mix screw seat may have been damaged is a good one, although it simply would not cause an engine to bog from 1/2 to 3/4 throttle. That is jet needles time to shine.... Not the idle circuit OR the main jet, unless light years off, will cause this. More likely, the issue with it staying running when seated is either a broken tip on the mix screw, a missing oring, or a pilot jet that is too large.
Ahhh screw it. Just order a new carb, throw this one in the trash, and start all over. Maybe you'll get lucky.
Pics are neat. I'll include one of a cb100 that got a full engine rebuild and TUNING at with 714 miles on the clock. The owner that has had the bike since new left it idling outside his shop with a full tank and forgot about it. Got a little warm. Then he tried to rebuild it himself. And then he brought it to me.