I have a new YS 63 that I was bench running. A total of 26 oz through the engine. It was running fine with nice thick smoke and bang. The engine stopped. I finally got the engine restarted but the throttle body no longer controls the engine speed. 1/2 throttle runs, full throttle runs, close throttle the engine speeds up. Move throttle arm to idle and the engine will drop of speed. There is no transition. It seems to be either on or off.

Never had a problem like this with any of my YS engines.

How should I approach this problem?