Notice the double, split jam nuts that Saito and everyone else uses on their 4-strokes. They are there for a reason. if your spinner (plastic or metal) does not allow the use of the factory-style locknuts, don't use it since that is an injury waiting to happen. With a 4-stroke, the operative word is "when" and not "if" when describing a bacfire.

Tru-Turn offers the proper locknuts to be used with their spinners, FWIW.