most likely what you are talking about is the charcoal canister.
It has to do with emissions.
Yep, emissions canister, for the gas tank specifically. When the gas gets hot some of it evaporates, since the tank must be vented to allow air into the tank as the gas level falls during use, the evaporated hydrocarbons come out the vent. The Enviro-Greenies don't like hydrocarbons floating around in the air, so the vent is routed through the charcoal canister. The charcoal absorbs the hydrocarbons while allowing air to flow in and out of the tank.
I've always wondered: at some point the charcoal in the canister becomes saturated and the canister needs replacement, so, how many moto makers actually stock and sell replacement canisters? I know they must have some stock, but who really has a NEED to replace a canister that most everyone tosses in the garbage? At what levels to manufactuers stock/ship replacements?
I await the day some government environmental agency scrutinizes the records of moto makers to see if this is being done. Sounds crazy I know. However, a few years ago I did see one of those flashing road signs on La Cienega in LA announcing, "Modified Exhaust Check Point Ahead", and I thought THAT was crazy too.
