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Product Review: Yoshimura DRZ400 Slip On System

When you think of off-road bikes, you don’t normally think of Yoshimura. After all, Yoshimura runs Mat Mladin’s AMA Superbike Championship winning roadrace team here in the United States, and Yoshimura has been identified with high quality street bike pipes and slip-on systems for many, many years.

The off-road world is changing, however, and high tech, water cooled, four-stroke, single-cylinder motors are now the rage in off-road bikes. Enter Yoshimura. A company experienced with not only pipe development, but engine tuning for four-stroke, high performance motors is an ideal fit for this new trend in off-roading.

To showcase their new DRZ400 products, Suzuki hooked up with former multi-time AMA National Motocross Champion, Mike Kiedrowski, to race in the Grand National Cross-Country Series on their new DRZ400. To modify the bike for racing, Suzuki logically looked to Yoshimura, a company it has a long-standing relationship with and trust in. Yoshimura was charged with the development of the motor and chassis of Kiedrowski’s bike, and, thus far, Yoshimura has developed various pipes, triple clamps, cams, etc. for the DRZ400.

We had a chance to test Yoshimura’s slip on system. We installed the stainless steel and aluminum slip on to the same DRZ400E we rode in stock form and reviewed in our article dated January 17, 2000. We liked that bike so much in stock form, we were anxious to test it with a more free-flowing exhaust system.


><br /><b>(Top) DRZ400 with stock slip-on removed.<br />(Bottom)DRZ400 with Yoshimura Standard Slip On installed.</TR></td>
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<p>Installation of the Yoshimura slip on was very straight forward.  The system comes with excellent directions, and the pipe is bent properly to fit perfectly with the stock header and bolt-on frame mounts.  All in all, removal of the side panels, stock system, and installation of the Yoshimura system took approximately one-half hour.  Of course, I tear apart a lot of dirt bikes (sometimes I think that’s what I do for a living), so it might take you a little bit longer.  Nevertheless, the system fit perfectly.  We weren’t done, however.</p>
<p>With the freer-flowing exhaust system installed, we needed to re-jet the carburetor.  The Keihin carburetor comes stock with a No. 142 main jet installed.  At Yoshimura’s suggestion, we installed a much-richer No. 165.  The carburetor is a tight fit, and it is difficult getting the carburetor removed and re-installed.  Once the carburetor is out of its boot, however, and you are able to rotate the bottom sufficiently to remove the cap under the float bowl, you can very easily access the main jet with a 6mm socket.</p>
<p>We took the modified bike out for a long trail ride involving some fairly tight and technical trails with rocks and moderate hill climbs, thrown in with two motocross tracks we found along the trail.</p>
<p>The first thing you notice about the modified bike, not surprisingly, is that it is much louder than the extremely quiet stock bike.  The noise level, however, is not unreasonable, and, in fact, is probably quieter than a stock Yamaha YZ400/426, for example.  The contrast is so noticeable simple because the stock pipe is one of the quietest four-stroke pipes around.</p>
<p>The next thing you notice is the complete change in the power delivery.  The low end throttle response is dramatically different from stock.  With the Yoshimura slip on and re-jetting installed, the bike absolutely rips off the bottom.  Literally right off idle, the bike pulls much harder than stock.</p>
<p>When revving the bike out, it appears to have a little bit more mid-range than stock, but about the same top end.  Remember, the stock powerband is soft on the bottom, with a strong surge in the upper mid-range that revs out extremely well.</p>
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This DRZ400 is one of Mike Kiedrowski’s practice bikes. It is equipped with
Yoshimura’s full titanium race exhaust as well as a carbon fiber water pump
guard and other trick parts. Note the street tire fitted at the rear for dyno testing.

The low-end power and throttle response make climbing technical trails a snap. I was following my son and a friend of his up a trail I was unfamiliar with (that they knew well). They were riding 125cc motocross bikes. I had no problem staying with these experienced riders. In fact, I felt like I was cheating. I could leave the modified 400 in second or third gear, and come out of very slow corners (almost a walking pace) without downshifting. Then, I could rev the same gear out on straighter parts of the trail (while the 125 two-strokes used at least two, and maybe three gears for the same situation).

This rock-strewn trail also increased my already favorable impression of the stock fork. The fork, which we have modified slightly with use of the rebound and damping adjusters provided by Suzuki, was very plush and controlled under these circumstances.

While we don’t have the exact weights, we can tell you that the Yoshimura slip on we installed saved approximately two pounds over the stock system. You can save more than 5 pounds with the Titanium Pro System (full exhaust including header). Here are the products currently offered:

Yoshimura DRZ400 Exhaust Systems

  • Standard Slip On – $249.95 MSRP
  • Race Slip On – $349.95 MSRP
  • Standard Full System – $479.95 MSRP
  • Standard Race System – $599.95 MSRP
  • Pro System – $669.95 (full titanium)

Overall, we were pleased with the performance of the Yoshimura slip on system. Particularly, if you’re in need of very strong low-end power and improved low-end throttle response, you will love the modification that we performed on the DRZ400.

When choosing an aftermarket company to modify your bike, look for a company that knows your bike well. We’re convinced that Yoshimura, due to its Suzuki/Kiedrowski connection, has more experience, and more dyno time, with the DRZ400 than any other aftermarket company. If you want a trick DRZ400, you can’t go wrong with Yoshimura.

Yoshimura can be contacted through their web page, www.yoshimura-rd.com, or at the following address and telephone number:

Yoshimura Research and Developement of America
4555 Carter Court
Chino, CA 91710
Phone (909)628-4722
Fax (909) 591-2198