I believe I got this tip from one of the posters on this forum. But I wanted to mention it again. I have shaken the muffler loose on my YS .91 AC sever times. If it hadn't been safetywired on it would be sleeping in the bean field. Well use teflon tape like you get at the pluming section of the hardware store. 2 times around seems to do the trick.
Wow is this one powerful engine! i only wish it didn't shake so much.
Sparky