[newday777]

The return cable missing shouldn't inhibit closing of the throttle blades freely.
Dirty bellcrank and associated linkage, dirty cable and/or how it is routed could.
The bellcrank spring provides for plenty of force to return closed.
Remove the pullxcable and service it. Reinstall it and try...

Another thing to check is for gummed grease or glue under the throttle tube on the handlebar. Found that yesterday on the 99A I have.
Anything on the bar or inside the throttle tube can cause a lack of free return of the throttle.