throttle does not return to off position when released

Yes. I had the same issue. Be sure not to tighten the nut too much, which holds the bracket of the handle. Be also safe, that it's not bent. The bracket should be in a 90-degree-angle. Check the bearing, which feeds the nut as well. It can be adjusted in height by turning. When adjusted too much in direction of the handle, the handle starts touching it while being turned.