4Strokes.com Suzuki Technical: DRZ400S and KLX400SR Upgrades by Matt Nelson on 4Strokes.com

Page 1 - Carburetor, Airbox, Jetting

Page 2 - Carb P/Ns, Exhaust Mods, Cams, Water Pump Fix

Page 3 - Compression, Suspension, Gearing, Guards, Removal

Page 4 - Tires, Taillight Mods


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)

Enlarged airbox hole

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.


Page 1 - Carburetor, Airbox, Jetting
Page 2 - Carb P/Ns, Exhaust Mods, Cams, Water Pump Fix
Page 3 - Compression, Suspension, Gearing, Guards, Removal
Page 4 - Tires, Taillight Mods

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