Cycle News Magazine
July 11th Issue #27 2001
Building The Perfect Beast/Almost
YZ 400F - and turned it into a street legal, working class dual sport machine. Its a time honored task: countless motorcycle magazines have published how - to articles,
explaining that going from dirt street is the best way because the dual sport bikes offered on the market at the time simply weren't up to snuff for hard-core off roaders.
Even when bike of the same brand and model are offered in dirt worthy and street oriented versions, the streeters usually lack the more sophisticated suspension components
(and usually better action) of the off-road bike, are hamstrung by leaned-out "smogger carbs and exhaust, and weigh severely pounds
more due to the switch gear and other DOT mandated items such as metal fuel tank.
Trouble is, attempting to get a tag for and off road conversion at your local DMV these days is like taking a trip through hell - you face a lot of heat, and you
can never be sure what'll happen when you come out the other side. So, far this year, we decided to go back to the old-school way of doing things - same as they
did in triumph's hey day: hopping up a street bike to optimize it for extended runs down our favorite singletrack.
There was no question that Suzuki's brilliant DR-Z400S was a good choice for such a refurbishing. Our 2000-model ES test rat was a sheer blast to ride around town,
constantly forcing us to check up our desire to go curb hopping or blast up and down the nearest staircase in front of the occasional building. Off-road, however, the ES just
couldn't quite run with its DR-Z400 sibling. For serious hammering, the ES forks and shock are under sprung, hampering high-speed control, and they lack the presence of
rebound-damping knobs,which are found on the off-road version (Suzuki has changed that for 2002). The fork and shock needed help. We also wanted more powerband,
last but not least we wanted to find a way to streamline the looks of the bike, giving it more of an aggressive off road aesthetic while maintaining its street utility role.
First things first, we placed a phone call to our pal Gary Jones and the folks at White Brothers, looking to get our ES model more legs - both in the suspension and
powertrain departments. Jones took in our bike and tore into it, handing the fork and shock over to White Brother's lead suspension tech Steve Searcy,
while Jones himself took apart the top-end of the motor.
Searcy jazzed up the suspension primarily by addressing the spring deficiencies both front and rear. In the case of the front fork, that meant ditching the stock
.43 kg springs in favor of higher quality Eibach .47 kg units. Also, since the ES model doesn't have a cartridge fork, Searcy went old-school route of tuning the damping rate via
an adjustment of the fork oil level. White Brothers suspension department uses Spectro oil exclusively, and Searcy chose 10-weight oil, raising the level in each leg to a measurement
of 130 mm from the top of the tubes: the stock oil level is 140 mm from the top. Adding a set of Race Tech's cartridge emulators is another hot route to take, although Searcy said that
the emulators do add a bit to the price of the job, and he did not feel that they were absolutely necessary.
Out back, the stock shock underwent a complete rebuild and revalve, with Searcy ounce again swapping an Eibach 5.7 kg spring in place of the stock 5.3 kg spring.
With the shock lacking a rebound adjuster, Searcy says that proper valveing is crucial to the damping quality. Knowing that our bike was going to spend more time in the dirt than
on the street, Searcy set up the shock to more closely approximate what Searcy calls "motocross style" valveing.
Here again the shock was rebuilt using Spectro oil Searcy elected to go with company's very light grade.
One of the highlights of any DR-Z400 is its engine, which provokes zappy throttle response with a milky smooth power delivery, making it one of the most
off-road engines you're likely to ever experience. Still its in our nature to look for just a little more, and we enlisted Jones technical expertise for some added snort. It came
in the form of two WB engineered parts: their all around intake camshaft and R4 exhaust muffler. The cam is designed to punch the intake valves open just a little higher and for a little
than the stocker, to broaden the power from the bottom end on up, producing a healthier over rev on top as well. As for the R4, aside from its good looks, the muffler is said to help
the motor breathe better, aiding throttle response without the added penalty of excessive noise. Furthermore, the muffler checks in at about 8 pounds lighter than the stock DR-Z400ES
muffler, Jones also placed a less restrictive Twin Air filter in the stock airbox.
Upon completing the engine, also saw fit to lower the overall gearing, canning the stock 45 tooth rear sprocket in favor of a renthal 48 tooth rear. An RK non O-ring chain also
replaced the stock O-ring unit in an effort to reduce frictional loss, freeing up every last available pony. One last thing: Jones also replaced our stock handle bars with trick looking
TAG Metals units adoring them with UFO handguards for added protection of both our hands and the bikes controls.
Finally, for added peace of mind, we turned to Suzuki's parts and accessories division for a couple items. First, we bolted on a DR-Z400E kickstarter set,
which provides redundancy in the starting category. Interestingly enough, we didn't even bother to fit the
accessory compression release, as the bike kicks over and lights up easily without it.
The last thing we added was a set of Suzuki's carbon-fiber engine guards, which bolt straight into bosses that are found on the frame and wrap around the lower
front of the motor, providing critical protection for the water pump, which is otherwise exposed to abuse from rocks and such,
the fit and finish of the guards was awesome
Unfortunately, the payoff of all these mods wasn't instantly gratifying, as we suddenly had to deal with a stumble that we picked up with our stock spring diaphragm carburetor.
The bike powered up rpm smoothly enough with a slow throttle hand, but whenever we would really nail it to get the burst of power, it would lurch and die - not a desirable condition.
We tried everything from adjusting the air screw to changing the jets to moving the needle clip.. We even called up Dynojet for one of their newly developed carb kits for the DR,
but nothing seemed to work. It was only by chance that we had access to another stock ES carburetor, which we pirated. With that carb, the bike ran like gangbusters, so we then
duplicated all the settings on our faulty carb back to stock. Once again we had problems, leading us to surmise that ours is some sort of a dud. A new barb is on the way.
Once we did get the bike to run properly, we dug the changes that we'd made to the motor. Thanks to the WB cam and gearing, the bike is more fun to gas up, with its added
mid-range and top-end. It pulls a lot harder than the stocker. And the R4 is surprisingly, really quiet, allowing us to ride the
DR around on the street with out feeling like we're being overly obnoxious
Suspension wise, the DR-Z is absolutely awesome for all but pro-level off-road racing. Both the forks and shock proved to be pleasantly supple in tight,
rocky conditions, such as streambeds, while they offered plenty of control and big-hit absorption at higher speeds, even with a 200-pound rider aboard.
All told, we feel that this particular hot-rod job was a success, as our DR-Z400ES is now just as dirt worthy as its off-road brother.
The fact that we can run this dirt bike through the tag line at the DMV makes it all the better
Photos by Jeff Hain
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