After reading all of this thread and the talk of copper straps, safety wire, etc., all I can say is you guys must have some severe vibration problems.

I've been running OS four strokes (every size except the .40 and the multi-cylinder models) since 1988, box-stock, and the only exhaust problem I ever had was trying to keep an extension fitted to the 120 Surpass muffler on a CG Ultimate to route the exhaust out of the cowl.

I have several pals running YS 91s (an AC and a FZ) with absolutely no issues. My new 91FZ is scheduled for the break-in stand Wednesday. We'll see...

Steve