It's a fact. RD's and all two strokes have a reversion wave as the piston descends and that wave is reflected back from the hard end on a filter to pass through the carb a second time picking up more fuel on the way through.
Contrary to popular opinion, reeds do not close instantaneously and much of the wave continues to oscillate back and forth in the intake tract. Reeds do reduce that reversion and resulting fuel stand off behind the carbs. For some reason RD's seem to be more affected than some other two strokes, so for decades now, people have avoided fitting hard backed filters to RDs.
Contrary to popular opinion, reeds do not close instantaneously and much of the wave continues to oscillate back and forth in the intake tract. Reeds do reduce that reversion and resulting fuel stand off behind the carbs. For some reason RD's seem to be more affected than some other two strokes, so for decades now, people have avoided fitting hard backed filters to RDs.