You show a Robin 35cc next to your nick.
GEBE just installs a bit of corragated flex stainless steel gas pipe and faces it down.
They say it kills about 2dBA. I can tell you for sure in about two weeks.
I have not been to a m/c swap-meet since last Summer but there are all kinds of sellers out, that offer all kinds of small mufflers. A 90 degree bend would be needed. gebe does have an aux muffler for the two strokes and I do believe they are working on having one for the 4 strokes.
Julia said that gas line flex made the R/S 35 as quiet as the Tanaka 32..and according to her it is very quiet. Quiet enough to seek up on walkers and pedal bikes. It cost $5, so I got it with my order that shipped yesterday.
I think the corrigation of the gas line breaks up the sound waves.
The only way to have quiet stealth is with a larger motor with moderate throttle. Air cooled engines ring their fins under power. On some older air cooled M/Cs the fins have heat tolerant rubber blocks wedged in the fins as dampers.
Once the engine is quieter, tire noise will be present if they have any open blocks...and so it goes.