2010 Kawasaki KX450F Fast-Aid Project Bike

January 31, 2011
Adam Waheed
By Adam Waheed
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MotoUSA’s pro-level test rider, Matt Armstrong, shares with us how he set-up his 2010 Kawasaki KX450F motocross bike. View the 2010 Kawasaki KX450F Fast-Aid Project Bike Video.

Considering the abundance of aftermarket motorcycle parts and accessories companies there are no shortage of options when customizing your dirt bike. From handlebars and pipes, to plastics and graphics, the sky (and your wallet) is the limit when it comes to modifying your motocross bike. For this feature we look at how MotoUSA pro-level test rider Matt Armstrong customized his 2010 Kawasaki KX450F.

Our speedy evaluator picked the KX450F as his preferred bike in the 2010 450 Motocross Shootout. In fact, he liked it so much he purchased one at Thousand Oaks Kawasaki just days after our test. For the most part, he was really pleased with the way the bike performed stock. But as a former pro, he knows exactly what he likes in terms of bike set-up. So he went about tweaking the powertrain, suspension and ergonomics, then added individual style that would make the bike even more fun to ride.


You’d be hard pressed to find a rider who says that the fuel-injected KX450F is lacking in terms of engine power. Both on the dyno and on track the Kawi is simply one of the fastest production dirt bikes you can buy. The only problem is that its snappy, hard-hitting powerband can wear out its pilot.

The Renthal Twinwall McGrath-bend handlebar  with soft Renthal waffle-style hand grips  sits inside a Pro Circuit handlebar clamp designed for better handlebar rigidity in case of a crash or tip over.
An eye catching gold-plated DID 520 ERT2 Chain  available at Motorcycle-Superstore.com  replaced the stretched out stocker.
Rather than re-pack the stock muffler we replaced the entire exhaust with an affordable Yoshimura RS-2 Comp Series Full Exhaust System  available at Motorcycle-Superstore.com .
(Above) The Renthal Twinwall McGrath-bend handlebar (with soft ODI waffle-style hand grips) sits inside a Pro Circuit handlebar clamp designed for better handlebar rigidity in case of a crash or tip over. (Below) Rather than re-pack the stock muffler we replaced the entire exhaust with an affordable Yoshimura RS-2 Comp Series Full Exhaust System (available at Motorcycle-Superstore.com).

“Stock the engine has so too much hit off the bottom,” said Armstrong. “It would spin the tire way too much and when it did hook up it was hard to keep the front end down. I wanted to mellow it out.”

In hopes of making engine power easier to control, we fitted the Kawasaki Fuel Injection Calibration Kit, available as an accessory at Kawi dealers. The tool fits underneath the front number plate and is plug-and-play easy to install. Based on our considerable time with this tool, we knew that the Hard Terrain power map would probably be ideal, and it was.

This map was designed to mellow out engine power at low-to-mid rpm in order to help the rear tire hook up on slick surfaces. It doesn’t necessarily make the bike slower, just easier to ride at the majority of throttle settings encountered during a moto. Of course if you want more power all you have to do is tug on your right wrist.

One of few squawks we have with the ’10 KX450F is how quick the packing within the stock muffler wears out. Rather than simply repack it, we fitted a Yoshimura RS-2 Comp Series Full Exhaust System (available at Motorcycle-Superstore.com). Not only does the pipe emit less ear-damaging decibels, it actually increases top-end power slightly. It also has an optional USFS-approved spark arrestor insert for those that ride off-road.

“The new EFI mapping along with the pipe smoothed out the power,” commented a satisfied Armstrong. “Plus mid-to-top ending performance felt a little stronger. I also noticed that the pipe added a bit of over-rev which really helps when you’re trying to clear jumps out of slow corners.”

Considering the short lifespan of the stock chain and sprockets we fitted up a more durable set-up from Renthal and DID. We stuck with the 13-tooth front steel countershaft sprocket but went one-tooth up in the back (better acceleration) with a 51-tooth Renthal 520 Twinring Heavy-Duty Rear Sprocket. The cool thing about this cog is that the center is made from lightweight aluminum but the teeth are CNC machined from steel so it’s durable against the strong twisting force of a 450cc Single. The sprockets are spun by an eye catching gold-plated DID 520 ERT2 Chain. Lastly, a more durable chain block was fitted from T.M. Designworks.


At 5’7” and 155 pounds, Armstrong is light, but still puts considerable load on the suspension based on his speed. Since he is smaller and lighter than the target rider for the KX450F, the suspension spring rates and internal damping settings needed to be modified to get the bike to fit him better.

“The fork was a little stiff. On the tiny stuff it would jump around and never really settle. Then as it went down into the stroke it somehow felt softer. When I landed off of big jumps it would just blow right through the stroke.”

After acquiring about 15 hours of riding time on the bike, one of the fork seals began to leak so we decided it was time to ship off the fork and shock to the suspension tuning wizards at Factory Connection. With service location on both the East and West Coast, Factory Connection is a one-stop-shop for all of your suspension needs whether you’re going racing or just need routine service.

A shorter McGrath-bend Renthal Twinwall handlebar was fitted to increase rider comfort. Armstrong complained that initial fork damping was too stiff when stock. Factory Connection made it much more plush and responsive feeling. With a few simple modifications Armstrongs KX450F was much easier and fun to ride.
With a few simple modifications Armstrong’s KX450F was much easier and fun to ride.

Inside the stock 0.48 kg/mm fork springs were retained, but Factory Connection installed different pressure springs that apply less force on the damping rod. This allows the fork to be more responsive over small chop. Internal damping settings were also tweaked to get the pistons to flow more oil at different parts of suspension stroke. Fresh seals were fitted and the fork was re-filled with its house-brand 5-weight fork oil.

The Hard Terrain fuel ignition map allowed the rear tire to hook up better yet also reduced the bikes propensity to wheelie out of corners.
The Hard Terrain fuel/ignition map allowed the rear tire to hook up better yet also reduced the bike’s propensity to wheelie out of corners.

The stock 5.5 kg/mm shock spring was ditched in favor for a softer 5.3 kg/mm coil. Furthermore the shock received FC’s Compression Piston Plate and High-Speed Compression Spring which is designed to be more reactive at high shock velocity – like when the rear tire encounters a huge hit and bump on track. Lastly the shock was topped off with 2.5-weight oil and then recharged with nitrogen.

“Way more progressive,” stated Armstrong in reference to the improved suspension action. “Initially it felt plush but as soon as I landed off a jump it got progressively stiffer so when landed hard it didn’t feel like I was going to break my wrists (laughs). The shock wasn’t too bad stock. But they made it feel plusher. It wasn’t as big of a difference as the fork, but it wasn’t too bad to begin with honestly.”

A common complaint smaller riders have with the KX450F is how big it feels. One way to make it more comfortable is to fit a different handlebar.

Kawasaki KX450F Fast-Aid Project Bike
10 Kawasaki KX450F Fast-Aid Project Bike.
DID Chains
520 ERT2 Chain: $91.99
Dirt Digits
Polisport Plastics: $150
Armstrong V2 Graphics Kit: $250.00
Geomax MX51 90/100-21 Front Tire: $60.99
Geomax MX51 120/90-19 Rear Tire: $73.99
Factory Connection
Fork Re-valve Service: $180.00 
FF5 5WT Fork Fluid: $26.95 
Factory Connection 5.3 kg/mm Spring: $109.95
Factory Connection Pressure Springs: $39.95 
Fork Oil Seals: $28.00
Fork Dust Seals: $28.00 
Shock Re-valve Service: $180.00 
GSF 3WT Shock Fluid: $17.95 
Shock Oil Seal: $30.00 
FC Compression Piston Plate: $19.95 
FC High-Speed Compression Spring: $17.95 
PRO EDITION Half-Waffle Motocross Grips: $8.95
Pro Circuit
Kawasaki Bar Mounts: $99.95
Renthal 520 Twinring Heavy-Duty Sprocket: $89.99
Renthal Twinwall Handlebar (999 McGrath): $107.99
T.M. Designworks
Rear Chain Guide: $24.95
Yoshimura R&D
Yoshimura RS-2 Comp Exhaust System : $494.99

“I’ve always run Renthal’s 999 McGrath bend because it is lower bar and because I use to run it when I raced Supercross,” said Armstrong. “I wanted to go with the Twinwall model because I hate when you fall over and the bar bends.”

The Renthal Twinwall Handlebar sits within a Pro Circuit bar clamp mount that is designed for added rigidity. As for the hand grips Armstrong slipped on a pair of Pro Edition half-waffle grips from ODI. The grips look fantastic in white and significantly increase rider comfort. Lastly, a fresh pair of Dunlop MX51 Geomax Intermediate tires replaced the out well-worn Bridgestone treads.

Matt has a knack for style so he ditched the stock plastics for a complete set from Polisport. The plastics are available from Dirt Digits and only cost $150 including the front number plate and fork guards. Armstrong then commissioned Dirt Digits for a full custom graphics kit with pre-printed number backgrounds. The kit costs $250 and since Dirt Digits has an artist on staff the sky is the limit when it comes to your personal design. The final touch was a custom seat cover from N-Style.
“I absolutely love my bike now,” Armstrong says. “I think it looks awesome. It’s cool to do something a little different. The lines are clean yet it still looks racy. All the things I did improved every area of the bike. From the handling, to the power and in the end it just made it that much easier and way more comfortable to ride. Sure there are some more things I want to do it but I just need to save up some more money first (laughs).”

Armstrong demonstrates his whip game aboard his 10 KX450F.
Without question, Armstrong’s ’10 Kawasaki KX450F is one of the sharpest looking dirt bikes we’ve seen this side of a factory racebike.