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Did you happen to adjust your right side controls recently?
Sometime people push the throttle tube too tight against the bar end and that will create drag.
You can also lube and make sure they are adjusted properly.
If you noticed it after installing your gas tank, it may be binding up underneath. Mine did. I had to lift the tank up and jiggle the cable around a little bit.
From your other post, sure your's is unhooked from motor.? Not sure what your setup is but I replaced my brake light switch a while back. When I took the clam shell apart, my twist grip slides off and mine had a lot of crud up in there. Since it appeared to be hard plastic turning on the chrome handlebar, I just cleaned it up. Fills great. Probably some silicon grease would do the job but I just think things like that attract dirt and other crude. Modern throttle and clutch cables slide in a nylon sleeve. If the get tight, they are worn out in a bend and need replaced. Just my opinion.
I agree with Texas, sounds like adjustment. Mine gets a lot of resistance if my idler cable is too tight. Sometimes the cables slip out of the cable holds on the carb when I'm messing around, that will do it too. I just loosen everything up, and start over.