No, not surging.
What I meant was that closing the throttle lever slows the engine down to some degree, but as the throttle becomes fully closed, the revs are still too high. Closing the throttle even further causes the engine to pick up speed. it only does this as the throttle is moved, not on its own, (surging)
Sorry if I was unclear!
Have got busy ploughing now, so it may have to wait for a while before I get back to it.
Will keep you posted though!