Kawasaki 400 turned 450!

Back in 2003, Suzuki helped revolutionize the world of ATV racing by introducing the four-stroke Quadsport 400. At the time, Suzuki and Kawasaki had joined together to produce the same machines under different colors and company names. The Kawasaki KFX 400 is exactly identical to the Suzuki LT-Z Quadsport 400 in almost every way. These ATVs are sporty and fast with an extremely durable motor. However, with the development of 450cc ATVs, the 400cc engine can’t keep up. This ATV was once at the top of the podium as a race machine, but it is now considered a trail quad. For this budget build, we wanted to bring this ATV back to its roots as a racer yet make it a blast out on the trails.

Left over from the Kawasaki and Suzuki alliance days, we found a KFX 400 that was still in amazing shape. We wanted to add power to the engine, along with some safety and handling items to make our older ATV feel more like a newer 450. If you think that adding a bunch of bolt-on mods will make your 400 act like a sport 450, you might want to think again. Unless you plan to spend far more than the used ATV is worth, it won’t be on the same level as a 450, but it will turn into a much better machine. We wanted to keep the modifications and bolt-ons as simple as possible, so we headed to Rocky Mountain ATV/MC to get all the needed parts for this project.


Increasing power from the durable 400cc engine was the first step. The lower end and valve train were all in great shape, so introducing a high-compression piston and cam shafts were a no-brainer. However, price versus gain made it clear that a full big-bore kit from Cylinder Works was the way to go. A new 434cc cylinder, a Vertex piston and Cometic top-end gasket are all included in the $529.99 Cylinder Works big-bore kit. The new cylinder looks completely stock. We gained a strong low- to mid-end power increase with the kit, and to finish it off we put in Stage 2 Hot Cams to add more power in the mid and top end for the intake ($143.99) and exhaust ($153.99) cam shafts. That completed the internal engine modifications for the build.

Next, we decided to throw on a FMF Powerbomb header and a Powercore muffler on the Kawasaki, which increased power through the whole spectrum. Now the engine is as strong, or stronger, than a stock 450 with a great throaty sound. With most exhaust upgrades, carburetor work is a must. We went with a jet kit from Dynojet that ran the project bill up another $47.99. Whenever you install aftermarket mods for the exhaust and carburetor, a new air intake will round things out. A Uni air filter replaced the stock filter for $23.99. We kept the airbox lid on this quad; with it off, it can make a bit more power, but it is also more difficult to jet and harder to get rid of the dreaded bog. With some extra effort, it could be made to work with the lid off, but we feel good about keeping it on.


Starting from the front of the KFX 400, we wanted to make the ATV feel like a very refined version of its old self. Renthal’s handlebar and grips replaced the stock ones, along with a Works Connection clutch perch for $155.85. After putting on a parking-brake delete kit from Works Connection ($19.95), we moved on to installing a new chain from Renthal to help put the power to the wheels, which ran us another $63.99. The last handling upgrade was a new set of ITP Holeshot XC tires. ITP knows exactly what an ATV rider requires from their tires. These tires grip hard to help turn the ATV easily and to make sure all of its power reaches the dirt. A set runs for around $581.92 and is worth every penny.

Adding style to an ATV has always been a popular thing to do. There was no exception with this upgraded ride. Psych MX Graphics was happy to assist us with throwing on a nice custom graphics kit on the KFX. We were able to incorporate the company logos that helped us with our modifications while having a great backing design. We didn’t stop there. CV4 provided some neon green Formed silicone coolant hoses, along with a high-pressure radiator cap.

Lastly, adding safety upgrades to this project was important to us. Protection against the known dangers of riding ATVs is always our first thought before we go riding. We decided to go to Tusk and installed a set of nerf bars for $99.99, a front bumper for $64.99 and a rear grab bar for $39.99. That way, the rider’s feet will have an extra layer of protection from harsh terrain. The last things we installed from Tusk were a front-brake reservoir cover, along with a throttle cover for $27.98.

When most people start a project ATV, they want to install products that help the power and handling of the machine. Some like to change parts just to give their ride a better look, but we had a goal in mind with our KFX 400 project. We wanted to make the ATV feel as much like a sport 450 as possible without spending a ton of money to do it. With the help of Cylinder Works and Rocky Mountain ATV/MX, we succeeded. The power upgrades opened up the Kawasaki from the low end to the high end of the power range. The handling upgrades gave the ATV a better riding position and a more comfortable feel. Finally, the KFX got a makeover with new graphics and other stylistic parts. If you want to modify your older 400cc ATV to feel like a 450, these parts are the way to go. Nearly every major product for this project can be obtained directly from Rocky Mountain ATV/MC at www.rocky mountainatvmc.com, or call (800) 336-5437 for more details.