Jerky at Mid RPMs

[AvalancheCCM]

Ever since I've owned this GZ250, the bike tends to bog down at middle RPM's. It runs and idles fine, but when I accelerate, it gets about half way through the RPM band and starts to jerk. If I am in a lower gear (1-3), I've found that if I keep the throttle at about 75%, it will eventually "push" past the jerkiness and accelerate rather quickly to higher RPM's. If I use the higher gears, sometimes it will do the same thing, but sometimes there isn't enough power to push past the jerkiness.

This is my first bike and I'm still new to carbs, etc. I've run Berryman B-12 through a couple tanks but it's not done a lot. It does get better about 15 minutes of riding but the jerkiness is always there. If I leave the choke half way out while I ride, it seems to help.

Before I start taking things apart, maybe I could get pointed in the right direction?