Note: These Suzuki DRZ400S modifications may also work on the 2003 Kawasaki
KLX400SR as well as other model dirt bikes.
The Suzuki DRZ400S is currently the best dual purpose bike on the
market. Stock I would say the DRZ400S is suited for 75% dirt, 25% street. My
goal was to make it 95% dirt, 5% street. Fortunately, Suzuki has made this conversion
fairly simple. I said simple, I didn't say cheap.
The reason this is all necessary is because in California the DRZ400E/Kick
is classified as a red sticker bike. That means it is extremely hard, if not
impossible, to make it street legal. Your only option is to buy a bike that
is already street legal and improve on it. If you don't live in California (or
other "Green" state) you would be better off buying a DRZ400E and
putting a dual sport kit on it for under $500.
Suzuki DRZ400S Carb and Airbox Mods (0-4000' above sea level)
The DRZ400S comes with a Mikuni BSR36 constant velocity carburetor. It comes
with this carb for one reason and one reason only, because it can be tuned lean
enough to be Environmental Protection Agency (EPA) standards. The only thing
you should like about this carb is that it has the ability to adjust to changes
in altitude better than the Keihin carbs.
First thing to do, regardless of what jetting/carb setup you choose, you need
to open up the airbox so the engine can breath. Remove your airbox snorkel under
your seat, and enlarge the airbox hole so it is a 3"x3" square hole,
then use zip ties to secure your CDI (black box) in front of the airbox hole.
When cutting the hole make sure not to cut too deep or you'll cut a hole in
your rear fender! If you enlarge you airbox hole more air will be coming into
your engine, causing it to run leaner. To compensate for the more air you will
need to rejet with one of the options below to add more fuel. More air with
the right amount of fuel equals more power! Do not open up your airbox hole
if you do not plan on re-jetting.
Suzuki DRZ400S Carburetor Jetting Options
Purchase a DynoJet Stage One jetting kit. These kits are designed for an airbox
that is not enlarged, so the main jets that they come with are not large enough.
You need to modify the kit, and enlarge the airbox. For a stock, or a modified
stock exhaust put in a 140 main jet. If you have an aftermarket exhaust use
the stock 142.5 main jet. Then put in a 25 pilot (2.5 - 3 turns fuel screw)
or the stock 22.5 pilot (3-3.5 turns fuel screw), you should be able to find
both the main jet and the pilot jet locally. The main value of this kit is the
needle and spring, they both work much better than stock. Put the needle on
the 4th clip position. This kit cost about $60 and can be purchased many places.
The DRZ400S comes stock with a 142.5 main jet, 22.5 pilot fuel jet, change
that to a 150 main jet, 27.5 pilot. The jets can be purchased from many motorcycle
shops. This option will cost under $15. This jetting option is better than stock,
but not even close to as good as jetting option one listed above. I highly recommend
jetting option one.
There is a reason Yamaha put a Keihin FCR carb on their YZ400, YZ426, YZ450,
WR400, WR426, and WR450. Yamaha did it for the same reason KTM uses it on their
bikes, and the same reason Suzuki used it on their DRZ400E, and DRZ400 kick.
The reason is because it is a great carb! For about $1,200 you can purchase
this same Keihin FCR39mm carb from Suzuki. You will also have to change your
throttle cables, intake and outlet boots, and velocity stack.