Throttle sticks?

Try loosening the throttle clamp and back tube away from bar end 1/16th" and tighten back up. Probably got dropped and jammed the tube tight against bar end.

Also make sure there is no paint / coating on the throttle end of the bars, and make sure the throttle tube is clean. The cable did not get pinched, did it ?

Very good tip, seen this happen several times.

Renthal Fatbars... on a KLX 140L?

You may have the same problem I had in 1987 with some Answer "cut-to-fit" steel bars. You used to be able to buy a handlebar at 36" wide and cut them to your preference (most are 32" wide these days). I bought a set, installed them without cutting and found out that my throttle cable wasn't long enough. The bike would stick WFO every time I turned the bars to the right.

Check to make sure your cable isn't getting stretched by the bars being too wide or the cable being routed improperly. I have a feeling that the Fatbar may be sized for a full-size motorcycle and too wide for that 140. How are they mounted? Adapters in the bar cradles?