The Doppler air filter that looks like a bulb intrigues me. I haven't tried one, but eventually I will probably get one. $46 or so. Does anyone know if they are quiet or noisy?
Here's what I did with the stock airbox, and it helped a lot:
(1) Carefully cut off the intenal 90-degree "snorkle" tube inside the airbox
(2) Reamed out the remaining opening in the rubber grommet to get it as close to the inlet size of the carb
(3) Opened up 2 holes in the far end of the airbox (so the air still goes thru the filter)
If I had thought of it before doing (3), I would have used a hole saw to cut in a single hole just big enough for the snorkel, and then put that it on the far end, so the rubber 90-degree elbow would block the escape of noise