OK… here we go. As I have never seen a 2005 640 Adventure, we are, for purposes of clarity, going to assume it is the same as ’03 - ’04.
1. Main jet.
You should have a 152.5 as stock. Remove this (the bowl cap is a 17mm as I recall) and install a 160 main jet; pay attention to the spacer that comes out with the jet. This is only a starting point, you may go up or down 1 or even 2 sizes for your conditions. They are the same main jets used in Mikuni HSR carburetors for Harley-Davidsons, which makes them available at just about any H-D dealer or custom shop.
2. Removing the vacuum cap from the carburetor.
Remove the fairing and fuel tank, you don’t have to remove the dash, simply tie the “ears” up to the handlebars.
Remove the 2 screws holding the cap on while lightly holding the cap down. Remove the cap, and gently remove the vacuum piston/slide assembly. Remove the spring and push the needle up and out the top of the slide.
Note the position of the parts; refer to your owners parts catalog for correct position.
Remove the clip (do this over a large table, maybe with a white bath towel on it… just in case you “loose” the clip) from what is I assume will be the 3rd position from the top and relocate it to the 4th position.
Obtain a drill bit, preferably a longish one, .110” to.125” in diameter and drill out the two vacuum ports in the slide, on either side of the needle hole, to the drill diameter. Drilling from the top is slightly better because the surface inside the slide is square to the ports; the outside has a radius that requires you to have a bit of drilling talent.
That’s all the mods… you can reassemble the carb. You can use your finger to help guide the needle back into the needle jet in the carb body, then insert the spring. Be careful when reinstalling the cap that you do not pinch or distort the vacuum diaphragm. Don’t over-tighten the cap screws.
The air box is easy… either buy or make a copy of the KTM high flow air box side cover. Do not remove the snorkel on top the air box… unless you plan to run a 41mm Keihin FCR and a complete Akrapovic system, or it’s equivalent.
Here is one I "hacked" out of some 1.5mm carbon fiber plate... actually cost more to make this than go buy a KTM one.
4. Stock muffler.
Remove the Supertrapp spark arrestor discs and end cap. Obtain a 1.5” hole saw (might be 1.375"... but I think it's a 1.5"
), find a wooden dowel that fits tightly in the center hole of the mechanical baffle… you need this to help center the drill. (Vrago’s bitchin’ idea )
Core out the baffle tube with the hole saw. A tube of about 6 inches in length comes out when the hole saw cut thru.
Reinstall the discs… the bike probably comes with 10 – 12 discs stock… you can add up to around 16 to suit your personal sound meter, but as I recall, 10 – 12 is more than enough for most folks.
A bike that sounds good is great… a bike that deafens citizens is not so good.
That’s it… I hope.
While you have the tank off... this is a good time to remove the stock evap cannister and hoses. Just run a regular gas cap vent hose into the hole in the fork stem nut... just like 99.9% of the dirt bikes, or get a spiffy one way valve from e-line... or whatever.
E-line one way vent