The 2009 Kawasaki KX450F had the makings of a great bike, but in the wrong order.

Dear MXperts,
When spending the summer at my grandparents farm with the wife and kids, the guy on the farm next door told me that he tried racing a few years ago but got hurt. He said he still had his 2009 KX450F, and if I wanted it, he would sell it to me for $500. When I walked into his barn, I lifted the tarp to find an almost perfect KX450F. I’d like to take it back to 2009 race specs. Can you tell me what you did to MXA’s 2009 KX450F?

The 2009 Kawasaki KX450F was only the fourth version of Kawasaki’s 450cc four-stroke. It didn’t get off to a very good start in 2006. The 2006 KX450F had a mellow engine that was pleasantly powerful but tended to rev up slowly. The deal breakers were the four-speed tranny (that was really only a three-speed), wallowy rear suspension, harsh Kayaba AOSS forks and a nagging tendency to stand up in the center of corners.

For 2007, Kawasaki pumped up the engine by 3 full horsepower, fixed the forks and added a fifth gear. Unfortunately, the five-speed gearbox was no better than the old four-speed box, because all Kawasaki did was add a fifth gear on top. Additionally, the rear suspension was still wallowy, and the handling still didn’t like corners.

In a strange move, the 2008 KX450F gave back most of the 3 horsepower it gained in 2007. With less bark, the engine became more manageable but not faster. With stiffer valving front and rear, the suspension was improved, but the handling didn’t win any converts.

Which leads us to your barnfind 2009 KX450. It was a totally new bike. It was fuel-injected (the 2006–2008 KX450Fs had Keihin carbs) and got refined plastic and improved durability. It had a great low-to-mid powerband and made the most horsepower of any 2009 450. Here are the areas that we worked on in 2009.

1. 2009 KX450F. It has a great engine and an awesome powerband but an atrocious transmission. It was geared too tall. The gaps between gears were too big, and the shifting was not confidence inspiring. We swapped the stock 50-tooth rear sprocket for a 51. Gearing the bike down lessened the gap between third and fourth, moved third gear closer to second and, most important, moved second gear down so that short-shifting was more accurate.

The best chain guide fix is to switch to a TM Designworks Factory Edition SX unit. It is light and bulletproof.

2. Chain guide. Switching to a larger rear sprocket led to the chain guide being quickly chewed through. The chain ate through the bottom chain guide in three hours, so we installed a bulletproof T.M. Designworks chain guide. While at it, we also installed a T.M. Designworks chain slider to prevent the chain from wearing into the swingarm.

3. Triple clamps. Kawasaki recognized that the bike had a front end push from center out in corners, so they changed the fork offset on the 2009 KX450F (from 24mm down to 23mm). It wasn’t enough. We switched to Pro Circuit’s 22mm offset clamps.

4. Axle nut. Hate is a strong word, but it’s not strong enough for our distaste of the cotter pin used on the rear axle nut. The MXA wrecking crew threw the cotter pin in the trash and ordered a Honda CRF450 self-locking axle nut.

5. Handling. In our opinion, the 2009 KX450 was a runaway train of a bike. It was tall, long and wide. It wanted to turn but hesitated in the center of corners and twitched momentarily. The fore-and-aft movement caused the geometry to be in flux at the moment you wanted to turn; it wanted to think about it for a little bit longer.

6. Linkage. For 2009, Kawasaki raised the swingarm pivot up 3mm. This fed in more chain torque to stop the KX450F from wallowing. We helped this even more by running a longer Pro Circuit link to lower the height of the rear end and stiffen the initial part of the stroke.

7. Rubber. Kawasaki must have gone to the vintage museum to spec the less-than-spectacular Dunlop D742F front tire. This was a very bad front tire.

8. Graphics. We think the graphics on our KX450F fell off going down the back straight for the first time.

9. Rear fender bolts. The two bolts on the underside of the rear fender, up by the airbox, were magic. They could disappear.

10. Overall. The 2009 KX450F’s powerband was easily the best part of the bike. But, and the list of buts is rather long, the transmission ratios were wrong, the shifting was spotty, the cornering was cranky, the layout was jumbo-sized, and the muffler was loud. The engine had us dreaming good thoughts. Reality was something quite different. But at that price, how could you resist spinning some laps? Enjoy your new bike.


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