Mark, Viton is pretty good material for many apps but exhaust coupling of a gas engine or a YS is not one of them. Temperature is too high. Teflon tubing is better standing up to heat just fine, but it requires clunky clamps to seal.....too stiff and it eventually leaks.

Turbo hose is pretty good. It's thick walled and heavier than desired but it does the job.

My solution was a thin walled, very flexible ceramic fabric impregnated with Permatex ultra copper. It has turned out to last 1000 runs and still going and only needs plastic tie wraps to hold. It doesn't get stiff with time and has not burned through yet, for good reason. Works as well on the YS too. One neat feature of this method is you can custom mold whatever shape you like. Curves, bends, bulbs, dissimilar diameters, whatever, are all straight forward.