Engine lurching?
 

So...I got my spiderbox back from the shop about 3 days ago...rode it a little, then I rode it for about 45 mins today in a loop in my backyard. I slowed down to a little more than an idle, and the kart began lurching back and forth? It wasn't backfire, but it was revving up like it was accelerating a little, and lurching. So...I don't know WHAT THE HECK is going on, but it certainly wasn't happening before I sent it to the shop. After a $175 bill at the shop, THEY HAD BETTER HELP OUT. lol

Any ideas/suggestions?

edit: Noting that I just replicated this. It seems to want to "go" when it idles. I think the idle screw is set too high. My dad doesn't want me messing with it :p
It will roll forwards about 2-4 inches, then roll back (driveway is slightly slanted). And it seems to rev up, rev down, rev up, rev down very slightly. After a while, it was visibly SHAKING the kart.... Could it be an idle/clutch issue?

It was the idle screw! False alarm, everyone! LOL.