My YS's and Saitos continuously loose stock mufflers. I tried teflon tape and loctite tricks. Did not help.
Then I switched to high pressure teflon (steel mesh covered) hydraulic tubings to which I attached stock
mufflers. This worked fine for sime time until teflon inside the tubes got melted and burned off. Next were
Hatori headers for tuned pipes,but those like to break off at the joint. In case of YS's 110 and 140 the stock
OS90 muffler is OK and stays tight,but arrangement does not fit all installations. Now I am planning to try either
Flexible mufflers to use with stock mufflers or Slimline mufflers by themselves. Which would better on the long run ?
Thanks in advance

The back of my muffler blew off a while back on my .70. I drilled and tapped a 6-32 hole for the pressure nipple straight into the exhaust pipe, then just above the threads, I did like the older Harleys ... I put a (#6) bolt through it. it works out fine, and I no longer have to worry about turning it just right to get the pressure nipple to face right and I don't burn my fingers adjusting the HS needle.

The stock mufflers (Saitos cast variety not the earlier one) WILL stay put either with Teflon tape or simply by tightening while hot-----not warm but HOT.

I have used both methods successfully from the 72 through the 180 and most all stops in between.
It CAN be done.

I resorted to a Slimline but while they will stay put easily they require modification (closing off one tube) and do not fit inside many cowls.
If you do not close off one tube the exhaust back pressure is not enough to give proper fuel tank pressurization.

Yes, in this example 'back pressure' is a good thing!

I have found the best muffler for a 4 Saito is a straight pipe-cut off the muffler fitting and braze a short piece of copper pipe (4-6") at whatever angle you need-forget pressure-most 4 strokes don't need it. Works great and you will love the sound. Also brace the copper pipe where it exits the fuse or cowling with a clamp lined with hi temp silicone.