7 Common Kawasaki KX450 and KX450X Problems (Explained)

The Kawasaki KX450 is a quintessential middle-of-the-road dirt bike with a reliable motor and stellar handling capabilities.

The Kawasaki KX450X is the competition package, with added versatility and track-ready durability.

This article explores the common problems with the Kawasaki KX450 and KX450X.

1. Weak Rubber Handlebar Mounts

One of the main complaints regarding the pre-2021-year model KX450 was its small, 7/8-inch handlebars.

While the 7/8ths handlebars were smaller than other mid-sized dirt bikes, the main complaint wasn’t that they were too small for the rider but that they were overcrowded by the various switches, buttons, clamps, grips, and levers as the available options increased over the years.

The 2021 model departed from the KX450’s classic design in multiple ways, including stock Renthal 839-bend Fatbars that give riders more room for their hand controls.

That said, the rubber bar mount inserts that came with these new bars are much less durable than the mounts that came on the crowded 7/8ths bars.

Riders often complain that the KX450s bar mounts are so weak they brake and fail after just a single bike drop, making them unsuitable for the aggressive, closed-track riding many KX450 owners bought their bikes to participate in.

“We didn’t really hate the 2020 Kawasaki’s 7/8th handlebars, but with all the switches, buttons, levers, grips, and crossbar clamps, the bars were running out of room. The big bars aren’t an issue, but Kawasaki’s wimpy, marshmallow-like rubber bar-mount inserts are. They twist and deform in even the smallest crashes. We replace them.”

2. Forks are Too Soft

Another common complaint with the Kawasaki KX450 is that its Showa front forks and their integrated shock system are too soft, not only for experienced and professional riders seeking to track race at high speeds but even for slower, beginner riders to lean forward on unless the rider is small and exceptionally lightweight.

“I know they changed the [fork] valving on the 17s. But that seems like an awfully low inner pressure combined with a high-balance chamber. Maybe the high outer pressure will hold the fork up, but it won’t start soon enough to keep it from sagging way too much.”

• The stock front spring rate is 5.0 N/mm, which is effective for lightweight riders riding flat track but too soft to be practical for landing on after hitting a big jump.
• Some more experienced riders opt to swap out the left fork spring for a 5.2, leaving the 5.0 spring in the right to stiffen up the landing support by just a hair.
• Pro riders who hit big jumps at high speeds upgrade their 450X fork springs to a 5.2N/mm spring on either side.

3. Poor Quality Clutch Plates (Pre-2021 Models)

One of the main complaints KX450 owners reported with their dirt bikes was finally rectified in 2021.

Since the 2017–2020-year models are still popular choices on used dirt bike websites, readers must be aware of the poor-quality clutch plates that plagued the KX line before the Japanese brand overhauled the 2021 KX450 and KX450X models.

• Before 2021, Kawasaki equipped the KX450 series with a spring system complete with a judder spring, a spring-wound metal disc designed to smooth the engagement of the clutch with the engine.
• Like many of the outdated judder spring clutch systems, the KX450 was prone to what we call “clutch juddering.”
• Clutch juddering on a dirt bike is when the flywheel and the clutch components don’t mate effectively during the engagement, typically at take-off.
• Kawasaki equipped the KX450 series with a judder spring long after the other bikes in its class moved on to more efficient clutch designs.

The improper alignment between the KX450’s engine flywheel and clutch mechanisms causes slipping and inconsistent connection, causing physical juddering while you ride.

Kawasaki finally rectified the issue on the 2021-year model by upgrading its clutch basket with 7mm clutch plates with angular clutch fiber segments better suited for transferring oil between the plates for smoother, more efficient clutch engagement.

4. Poor Rear Brake Performance (2019-2020 KX450 Models)

Another essential upgrade to the 2021-year model Kawasaki KX450X was its smaller yet more effective 240mm rear brake rotor.

Even the smaller KX250 model was given the more effective rotor in the past, but for some reason, the standard KX450 wasn’t given the same treatment.

Kawasaki stocked the KX450 models with an oversized 250mm rear brake rotor, adding extra weight to a bike geared for dirt track performance, racing, and stunt riding.

Additionally, the jumbo-sized rear brake rotor lacks dynamic performance, fluctuating between not losing stopping power and grabbing too powerfully to be effective for serious dirt track riding.

Motocross Action Magazine had this to say about the KX450’s rear-brake performance after their test ride:

“The big rotor lacks modulation. It is too grabby. There are no brakes, and then there is too much brake. We ground the brake pad’s leading and trailing edges down at a 45-degree angle which downsized the pads to ease their interaction with the rotor. We are surprised that Kawasaki’s engineers didn’t spec the smaller 240mm rotor they put on the 2021 KX250 and KX450X.

“[Furthermore] The rear brake pedal can be adjusted upward but not downward. To cure this, we hacksawed three threads off the bottom of the threaded master cylinder rod to give the pedal more downward free play; that way, a boot can touch it without locking up the brakes by accident.” 

5. Plastic Components Break Easily

One of the problems commonly reported by owners of the Kawasaki KX450 and KX450X is the lack of durability regarding the plastic components, especially considering that the KX450 is intended for track jumping and motocross racing.

The plastic guards are known to crack, not just from sliding across the dirt but sometimes just from the impact of landing a jump.

The KX450 and 450X also include a plastic front number plate so riders can display their information during competitions.

Consumer reports and test ride articles reveal that the plastic number plate on the front of the KX450 cracks easily.

A cracked number plate is more than just annoying; it can eliminate pro riders from competitions, depending on how severe the crack is and whether or not it hinders them from displaying the competition qualifications accordingly.

Finally, the KX450’s plastic radiator arms are also prone to developing vertical cracks, which can cause serious problems.

More durable aftermarket parts are available for these components, but many KX450 owners feel cheated when having to replace plastic parts on a bike specifically designed for hardcore dirt riding.

6. Chain Guide Wears Fast

The most common consumer-reported problem with the Kawasaki KX450 and 450X is how quickly the bike’s chain guide roller wears out early, sometimes after a single hard dirt riding session.

Dirt bikes hit the ground often, much more frequently than street motorcycles.

Therefore, exposed dirt bike components like chain guides need to be able to take a hit and keep functioning.

• The roller guides the moto’s chain to keep it on track as it rolls off the countershaft sprocket.
• If the chain guide brakes, the chain can whip back and forth, risk injury to the rider and nearby track riders, and cause a competitor to be ejected from the race if the judge or ref deems it a hazard.

 “I wore through the stock chain guide and slider [after just] 6hrs [of riding] when [the KX450 was still] new.” 

“I rode the bike one long weekend and ate through the chain slider and into the rear swing arm. Needless to say, that cheap chain is gone, and the new slider is on the way.”

“The chain guide doesn’t last long at all. Stock ones, anyways. TM Designworks makes one that will last, a bit pricey, though.”

Again, while more durable aftermarket replacements are available as upgrades for the KX450 and KX450X, the fact that such a critical component is so susceptible to such early wear is disturbing to riders who bought their bike for its intended purpose of aggressive dirt track riding.  

7. Bolts Strip and Fall Out While Riding

Another common problem with the Kawasaki KX450 and KX450X models is the low quality of the hardware bolts. Riders frequently report that the KX450’s hardware strips quickly, even when minding the torque levels outlined in the owner’s manual.

While bolt vibration and loosening are possible on all dirt bikes due to the thumping nature of their motors, there is no shortage of consumer reports claiming that the issue on the KX450 and 450X isn’t the vibration.

It’s the bolt’s thread stripping during routine maintenance and losing its ability to lock in place.

As you can gather from the following KX450 owner reports, the solution is to apply a fastening solvent like Locktite to your hardware upon reinstalling after a  routine service.

“Also, check [your KX450’s] sprocket bolts after every ride. I Loctite all my bolts.”

“Don’t get heavy-handed on the [KX450’s] oil filter cover bolts, as it is easy to strip the thread, especially the top hole.”

“I don’t even touch the [KX450’s] small drain plug when changing the oil. That plug only lets you drain a minimal amount of oil, so I don’t think it hurts anything not to drain that part of the engine. I also Loctite the bolts for the rear sprocket, along with almost every other bolt I take off. Still, the kickstart bolt will occasionally back off.”

Pros and Cons

Pros 

• Fair Price Contrasted with the Competition.
• Rugged and Reliable Overall
• Remarkable Cornering and Rideability
• Efficient Stopping Power
• Sleek Chassis
• Straightforward 450cc Dirt Bike Concept
• Looks Hard and Stylish.
• Fun to Ride 

Cons

• Weak Rubber Handlebar Mounts
• Forks are Too Soft
• Poor Quality Clutch Plates (Pre-2021 Models)
• Poor Rear Brake Performance (KX 450)
• Plastic Components Break Easily
• Chain Guide Wears Fast
• Bolts Strip and Fall Out While Riding
• Radiator Leaks/Bike Overheating

What Do the Reviews Say?

“Setting up the suspension correctly makes a huge difference. With the reduced compression damping, the KX450X felt much better. Bump absorption improved, and the motorcycle felt a lot more planted. That gives me more confidence to ride at my ability. The side-effect was in the faster sections. When hitting small jumps or bigger whoops, the suspension rebounded too quickly and bounced back at me. The tech went one click in (stiffer) on the rebound, front and rear, to fix that. With this change, the suspension felt great at all speeds—no other mods were needed.”

“The 2021 Kawasaki KX450X has a high-speed motor with a broad powerband. Its linear power delivery works nicely in an off-road environment. The slightly lower gearing of the 450X kept me in the powerband’s meat and from stalling the bike in most technical sections. Just like the MX version, the X comes with three couplers with different engine mapping. Surprisingly to me, I preferred the most aggressive map/coupler. I thought it would feel too aggressive, but it didn’t, as the overall nature of the motor is smooth. I prefer the aggressive map because it provides a little more torque and bottom-end power. That really helps when riding at low rpm through the tight terrain.”

“Electric starting and kickstands are essential additions. Kawasaki has been a bit late to the e-start game, and it is even more critical on an off-road motorcycle than a motocrosser. When I first saw the kickstand on the KX450X, it looked like it stuck out quite a bit and would be in the way. Once underway, I never even noticed it. I was unaware of the kickstand with my boot or when bouncing through the hoops and over jumps.”

SOURCE: 2021 Kawasaki KX450X Review: Off-Road Motorcycle Test (14 Fast Facts) (ultimatemotorcycling.com)

What’s the Resale Value of a Kawasaki KX 450 and KX450X?

What are Some Alternatives to the Kawasaki KX 450? 

Related: 8 Common Kawasaki KLX300 Problems (Explained)

Sources:

2021 Kawasaki KX450X Review: Off-Road Motorcycle Test (14 Fast Facts) (ultimatemotorcycling.com)

2019 Kawasaki KX450 For Sale in Loveland – Cycle Trader