I just put a UNI foam air filter in my '72 cb500f...ohhh man, what a difference! The bike can actually kick my head back now! It was definantly a great 24.95 investment. although i have not tried the 4 k&n cone filters, i think this would be a cheaper, but less effective rout to gaining some cheap horsepower. I did have to adjust my carbs after, and getting all the foam filter oil squeezed out of the filter was a little of a pain. but hey, it was my first time. just passing the word to anyone interested.
