Ok here is something to check. Siince you took the thing apart, you may have pushed the throttle tube too far onto the handlebars, thus causing the end of the handgrip to rub on the end of the handle bar. No matter the problem is obviously in the throttle tube assembly. If that isn't it you're gonna have to just keep looking for what is rubbing. It may well be that you are not installing the cable properly and it is binding in the throttle. Take the cable out and see how free it turns ..
zilla
zilla