Hmm. I'm not a phbg expert, but I did experiment a lot tuning my 103 with a phbg when I kitted it, unfortunately shortly after I got it all tuned perfectly a circlip failed, thus ending my experiments with phbgs for a while....
Anyhow, one thing to consider with multi-circuit carbs is that throttle position dicttates fuel mixture. The whole point is to have different mixtures depending on different rpms, so you can have a nice rich mixture when you're going super fast, but not so rich that you bog out when you're going slower.
So if you're stopped and you open the throttle all the way, you're gonna be jetted for high rpms.... not off the line, thus, you'd bog. However, if you use the throttle with more finesse, opening it gradually, you'll have better engine response.
You may already know all this and be suffering from a totally different problem, don't mean to tell you stuff you already know, but just make sure you have this in mind.... also I don't know what size carb you have, if it's huge 19-21 or something this problem would probably be more pronounced (and maybe feel like having your motorcycle in 3rd gear when you're only going 20mph, y'know?)
best of luck.