Sticking Throttle

Hello everybody,
This is my first post so please, bear with me. I have a Huffy Cranbrook with a 66cc Grubee SkyHawk engine kit, and this was my first build. I finally got everything set up today, and i went to check everything out. I removed the carburetor, it's the stock carb, and i saw the butterfly wasn't down all the way. I unscrewed the top of the carb and the removed the springs, and the butterfly. I got the indents in the butterfly lined up with the notches inside the carburetor. I put the butterfly back in but it still wouldn't go down all the way, but I can pull the throttle and it raises a little bit and then returns. I took the bike for a test ride and it was stuck on full throttle. I hope it's a simple fix but I have no idea what it could be. Any help would be appreciated, thanks.
P.S. Perhaps it's the throttle? but i don't know how to adjust that either

Thanks a lot guys! Decoherence, you were pretty much right. Turns out I tightened down the throttle assemble too much so it created a burr, which stopped it from returning to idle. I just sprayed some WD 40 in there and loosened up the two bolts holding the assembly together and whala! Works like a charm.

Alright, I've got another problem. Like I said before, I have a huffy cranbrook. It appears the chain is rubbing on the white wall part of the rear tire. I'm not sure the measurements of the rear tire right now, but how can I fix this? Is there anyway I can space the chain a little bit further away from the tire? My sprocket is lined up perfectly with the engine sprocket however, so I would not want to jeopardize my alinement. And if i have to buy a thinner rear tire, would that mean buying a new rim and a new tube? One more thing, i really like the look of the whitewalls, does anybody know where i can get a set of thinner whitewalls?

Thanks for your help guys. Acraze, that would be great, if you can tell me how to do that, then my problem would most likely be fixed. And richirich, that's how i have it now. Before i flipped it around it was rubbing too, and i thought flipping the sprocket would solve the problem, but it's almost exactly the same. Go figure. One more thing, does anybody have a thumb choke? Because that's what my kit came with, even though it wasn't on the parts list on the site. I can't figure out which is on choke and which is off choke. I took the carb apart and looked in through the opening and moved the thumb choke and there was nothing that restricted/unrestricted the airflow other than a TINY hole that leads to a cylinder with a small piston like thing that goes up and down as you move the thumb choke. I can only start and run my bike when the choke is in a certain position, so either it won't run off choke, or it won't run on choke. Either way is a problem. However, if i have been running it on choke this whole time, what would be a normal top speed? Because i can hit like 27mph on my engine and its not broken in yet. Would this be normal for running on choke?