Well as a temporary fix, i would move the throttle linkage on the carb all the way back till the carb is completely shut. Then i would turn the idle screw clockwise until there was a .5-1.0mm opening in carb window. That should stop the linkage from going too far back. But im my case, my low speed needle went bad on my carb and now its inadjustable. So long story short, i need a new carb for that engine but i've gotten great use out of it and plan on getting a new one anyway. But try that. you may need to loosen your low speed assembly and retighten it but just use caution as all the parts can go out of wack if messed with inproperly. See if that works. good luck with it.