When it comes to Harley's they have a California only evaporative emissions system on top of the 50 state regular emissions package (note on the spec and pricing pages it is an additional cost item). It consists of a carbon canister to collect fuel vapors and a purge valve that releases the collected vapor back to the intake when the engine is running. Basically the same thing cars have had for decades, but for whatever reason the US EPA doesn't require them for motorcycles. California does. The fuel tank vent hose that just dumps vapor into the air on 49 state bikes is connected to the carbon canister on Cali bikes.
Jerry