Can you remove (Dremel tool) the cup washer on the rear of the clamp screw, then unscrew and straighten it?
Look on the rear of the magneto plate – see a screw (mabe two, I forget) there? Loosen the screw or remove it and the spring under it – apply WD40 into the hole and work the mag lever. That screw is a tension device to keep the lever from wandering when running. Old oil or grease is gummed probably and holding it tight.
Good luck. JW in Dixie