Last weekend during some routine service I completed the "airbox mods". I removed the snorkel and took the vacum line off the flapper. I then plugged that line with a golf tee. I did notice a difference in the sound. However, the flapper still seems to be flapping. Possibly even worse than before. There's no noise for the first few minutes but once the bike warms up it flaps a lot at low speeds. I haven't noticed any performance problems but the noise is still irritating. Is this normal? I might plug it back in just to eliminate the noise.
