I think it was the manual that came with my Peugeot BB1st (1960's) that suggested that the test of a non-clogged exhaust system is to hold your hand a few inches from the exhaust outlet and feel the series of sharp puffs on your palm. Perhaps it's the oil or the characteristics of the engine itself, but two-strokes tend to have a rather wet exhaust product that distills out its liquid in the muffler and especially right at the outlet, where for some other unknown reason it hardens into tar. You may find hardened pebbles of carbon inside, but it's mostly important to dissolve out the tar.
M Kinsler