Intake
From Suzuki DR650 Wiki
On the 96-2008 DR650SE's the intake system is the most restrictive part of the motorcycle in overall performance and smooth operation. In stock condition the air box and it's rubber intake "snorkel"(14) severely restrict air flow capabilities through the engine. There are a host of mods that have been done to increase air flow like removing the snorkel, removing the air box side cover (6), removing the air boot screen (5), modifying the top of the airbox Other air flow improving techniques involve adding one or multiple filtered vents, velocity stacks or just plain drilling holes in the plastic box. Whatever mod you decide to do requires the proper carb jetting to keep the air/fuel ratio at the proper levels. Standard on the Mikuni BST 40SS carb is; main 140, pilot 42.5, needle 6F19 clip on 3rd slot (Australian, Canadian and UK needle). All US models use a 6F23 fixed clip position jet needle and a Y-5M needle jet. The most popular jetting kit for the stock carb is Dynojet Research's kit. Other options are Factory Pro's kit... this kit is based on leaving the air box in it's stock form. There is a ton of information here on these and other jetting mods for the stock CV carb.
When swapping info with other DR riders do not forget the size difference between Mikuni and DynoJet main jets ie a Mikuni 145 is roughly equivalent to a DJ 155
Of course if you really want to boost performance, throttle response and engine smoothness you have to remove the CV carb and replace it with a direct operated slide carb like Keihin's FCR series carb or Mikuni's TM series carb. For the super industrious there is no doubt a fuel injection system would be the ultimate addition but the work required to fab your own system would be a large undertaking.... starting here.
[edit] Links that can help
- Kientech Engineering's intake page
- Keihin's web site for the FCR-MX
- Factory Pro's CV carb tuning site
- Sudco International's catalog
- TwinAir foam filters
- Multisurfacemotorcycling.com's BST diaphragm vent filter kit (UNI Filter)
(EDIT: The information above was supplied by mx_rob. There is an important link that he has omitted, likely to avoid any appearance of self-serving intentions. Since this list would be woefully incomplete without it, I'm happy to put it here. It details all the efforts Rob has put into engineering the FCR-MX carb swap, and all he's done to "get it right". mx_rob's homepage -Krusty117)
Removing snorkel, drilling slide, and installing 2 small thin washers under fixed US needle had a very noticable power kick to my 06 DR650.
