How often do the two halves ever spin on the rubber spacer in the middle of them? Took my burb in to have the timing and carb fine tuned, and my mechanic (really good guy, knows his stuff) says it looks like the two halves have spun. He could only get my timing set at 22* /forums/images/graemlins/shocked.gif instead of the 8 or 12 or what ever its supposed to be(but that is according to the timing marks, its actually set correctly though). He got is all running right, its just that the marks don't line up. So has anyone ever hear or had or seen these things spin?