So the corrosion (rust) from inside the throttle cable was the problem. Every time the throttle was turned, thereby moving the cable, rust was rubbed off and collected at the bottom of the shielding/housing, eventually packing tight enough to seize the cable with the slide in the "full throttle" position. Cleaned and oiled, the cable moves freely, enough to allow the engine to throttle down. Replacement cable ordered. Runs great, 1 kick. Thanks fellow enduro enthusiasts.