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P.J., Technician
Category: Motorcycle
Satisfied Customers: 750
Experience:  10 years as a mechanic and fabricator in a privately owned, local, custom bike shop.
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Sounds like something is knocking in my air filter

Customer Question

Sounds like something is knocking in my air filter
Submitted: 1 year ago.
Category: Motorcycle
Expert:  P.J. replied 1 year ago.
The noise you hear is normal and is nothing to worry about. It is annoying though. The noise is caused by the pressure reversion that happens inside the intake and behind the throttle plate. The pressure reversion is caused the by the camshaft overlap between the intake and exhaust stroke. The throttle plate in 100% sealed when at an idle and the pressure wave causes the throttle plate to "smack" against the wall of the intake. The noise is typically pretty hard to hear with the stock breather assembly as it is also designed as a silencer. Aftermarket breathers, as well as Screamin' Eagle breathers, are not designed as silencers and do very little to stop the noise from being heard. I hope this helps. Thanks, P.J.