I talked to Toomey today and found this on their web site. Very interesting......
"On the Banshee the most out-of-phase area is right before it synchronizes with the pipe.... so 4000 to 5000 rpm, then at 6000 it starts harmonizing it's pumping action and you feel the pull in the handlebars!
What is happening actually is that this wave is being reflected back and forth inside the intake tube (tract) regardless of the fact that the air is only moving in one direction, the wave, which has little if any mass, can travel in both directions and does... Each time it does, it passes the needle jet and when it does, it pulls fuel. When this happens there might be a piston stroke with several helpings of fuel instead of just one, therefore it is rich.
The intake tract is too short, and this is one reason why it is a bad idea to put the little K&N filters on the back of each carb, effectively shortening the intake tract even more.
Because this is an RPM specific phenomena, it cannot be "jetted out" because conditions change in response to RPM, not throttle position. If it was at a particular throttle setting, then we could easily say, that at this setting, certain circuits are active and make adjustments accordingly, but it is not. Raise the rpm a little and it goes away. This is one of the reasons Yamaha chose to put the "cross-over" tube between the intake manifolds. This makes one intake tube think it is larger than it really is (as far as sound propagation goes) therefore lowering the frequency of the sound wave, dampening the effects. You can try this experiment yourself, just remove the crossover tube and be sure to plug up the holes in the intake manifolds from which the tube came, then ride it. You will see the difference!"
Reference:
Toomey Racing USA Retrieved August 24, 2005, from:
http://www.toomey.com/