Old School Engine Driven Welder Loses RPM When I Strike an Arc.

[Iplayfarmer]

The kill switch is on the points cover. I doubt that is what the little silver knob is for. I do find out that the silver knob is some kind of plunger switch. When I pull on it it comes out.

Here are a few more shots if the machine.

 

[Joe Blackeby]

Howdy, the white button (above left pic) is the kill button (grounds the points)
Every gas or diesel welder I was ever around would have an "exciter" that would increase the rpm of the engine produceing more power. Trace back the part in question. Usually a solonoid to move throttle linkage.
Maybe it has a compression release for starting in the cold. HTH, JoeB