#20 is the air box cover so you can wash up the air box area with the filter removed. I am not sure about #2. It is listed as a Throttle Cap. Could it be some type of air restriction device? It is only shown on the EU parts fiche. It is not shown on the US parts fiche. I did not have either one of those when I purchased my 09 450. I have since picked up #20.
all the above answers are true. But when You see 2 components on the "same level" on a drawing like Husaberg, they are complimentary pieces (like #2 and #3 in the example above.
The #20 component is "Optional", it is not shipped with the bike. It was sold in Husaberg Force catalogue.
Wow, I never would have guessed Husaberg had such a device to restrict power. What does #2 do, cut power in half?
A few years ago a buddy bought a new Husky TE 511 to ride in the street & the dirt. On his 1st ride he said it did not have any power. He changed mapping, exhaust and some other things to get it so it was rideable. I guess all the manufacturers have to do what it takes to meet government regulations in order to sell their machines.