Jeez, It's like the Bermuda Triangle. Loaded Container Ship Leaves Galveston bound for Portland, Maine and disappears. Wow. Mystery. Then they tell us it was a new crew, captain drunk, ship overloaded and heading into a Hurricane, all never mentioned in the original news item. No Mystery, simple explanation.
Just a few little itty bitty facts missing from the original post.......Throttle stuck open, pulled the clutch, killed the engine. There's the answer, wide throttle, no load, hence major mechanical abuse. It ain't gonna be cheap. Get the spanners, arrange finance. Wire up another simple on/off switch that doubles as a magneto cut out. That way you have a primitive anti-theft device and don't need three hands to bring a runaway to a halt.