with the lever travel that's left, do you get the engine up to max speed ?
on my TG1860G, the lever appears similar, with only about 1/4" travel before the engine speed picks up, and at the carb end of the throttle cable, it is clamped to the throttle plate...
where the governor spring, etc. are connected.
maybe that clamp is/was loose and allowed the end of the throttle cable to slip ?
Pete