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TPI valve works with your air box lid to add air when you need it, and keep the intake stock when you don't.
2 5/8" square TPI valve filters air and vent size is adjustable.
Comes with red fine filter, black medium filter, mounting hardware and instructions.
One TPI valve is adequate for most machines but for machines with engines 500cc and over, or with highly modified engines two valves work best.
Available at http://rockymountainmc.com for $17.99

What do you do if you don't have an airbox lid?

A filter to protect your filter, which is a two stage filter anyway. Hmmmm. Add a filterskin to your filter and now you won't ever need to clean the air filter again. Of course you will not get any air into the motor, but hey, you will have a clean filter.

I predict the next product will be a pre-pre-pre filter, so the 2 stage filter, the filterskin, the airbox lid filter all stay clean.