engine only idling

[BlowingOldBoots]

They are very common on drilling rigs where they are fitted with Alison Gearboxes.

Typically used to power truck (or skid) mounted high pressure pump units for pumping cement slurries, fracture fluids to breakdown rock formations and stimulation fluids to clean up pore space.

All are fitted with a "Rig Saver" which is no more than a glorified shut off valve to the air intake. You do get "Rig Savers" which also shut off fuel.

The "Rig Saver" can be tripped manually by throwing a lever or remotely by dropping out a solonoid (pneumatic or electrical powered).

Your friends engine may have such a solonoid valve and the electrical connections could be the source of the activation so check both air intake and fuel supply for shut off valves, even though you state that the engine still starts.

Post Posting Edit: I am pretty sure the "Rig Saver" is also linked into a governor on the engine so that any over speed shuts it down. The two strokes are quite high reving engines so maybe they need to have this protection as the the difference between high reving and destructive reving might be quite small, so something else to check for.