Are my expectations too high?

What carb is on it? The reason I ask is I'm dealing with the same issue right now (stumble at the hit of the throttle) with my 950 XP carb. After a lot of tuning the right way (shooters, cams, mixture screws, etc), my guess is it has something to do with the controlled air-bleed feature (I don't recall the correct name for that thing) near the carb stud...or at least that is where I am looking next. I have a friend at the track that fought the same issues with an XP carb, and the only way he found to fix it was to close the "air-bleed thingy" and adjust the idle the old fashioned way.