On a bike like a TZ250, you can actually see a fuel standoff behind the carbs at certain revs. It's the resonance effect.
MOTA is a piece of simulation software for 2 strokes and one of the things it does is to create a graphic of waves in each of the ducts (intake, transfers and exhaust). It is amazing to see that the pressure waves oscillate 3 or more times even at high revs. That means that the pressure wave is basically going in and out. Think of that as pulses back and forward. Each reversion is smaller than the one before it, but it's easy to see how it would screw up fueling.
I hear about helmholtz resonating air boxes but have no reason to believe that any manufacturer was doing that sort of analysis back in the day. What they did want was smooth flow and a still air box is the way to get that. That's also why many vehicles have a plenum chamber in the intake system design. Not so much to make it work really well at one rpm, but to make it work at all revs.
The other advantage on a still air box is that it is essentially not affected by cross winds or airflow past a rider's leg which often causes issues with pods and stacks. And that's why they typically have the intake in a relatively still area like under the seat.
MOTA is a piece of simulation software for 2 strokes and one of the things it does is to create a graphic of waves in each of the ducts (intake, transfers and exhaust). It is amazing to see that the pressure waves oscillate 3 or more times even at high revs. That means that the pressure wave is basically going in and out. Think of that as pulses back and forward. Each reversion is smaller than the one before it, but it's easy to see how it would screw up fueling.
I hear about helmholtz resonating air boxes but have no reason to believe that any manufacturer was doing that sort of analysis back in the day. What they did want was smooth flow and a still air box is the way to get that. That's also why many vehicles have a plenum chamber in the intake system design. Not so much to make it work really well at one rpm, but to make it work at all revs.
The other advantage on a still air box is that it is essentially not affected by cross winds or airflow past a rider's leg which often causes issues with pods and stacks. And that's why they typically have the intake in a relatively still area like under the seat.