Ian,
That is correct, there was no valve lift mechanism or magneto kill circuit fitted by the factory. Generally they are setup so that when the throttle is fully closed they cease running. The throttle was either (initially) a lever type or a twist grip with a friction device. Either stayed where you left it, so you do not set a low idle setting with the throttle stop on the carburetor, like you would with a more modern spring return carburetor. The sring above the slide only ensured that the slide returned to the closed position as the throttle cable was slacked off.
-Doug
