8 Common Kawasaki KLX300 Problems (Explained)

KLX300 is designed to handle both on-road and off-road riding, with smooth and flexible power delivery, a six-speed transmission, and long-travel suspension.

It also has a low seat height, a lightweight frame, and a digital instrument panel, making the KLX300 an excellent choice for beginners, commuters, and adventurers who want to explore the trails and the streets.

That said, like any machine, the KLX300 has been known to cause some common problems for its owners and riders over the years. This article explains those problems and how to get back on the road.

1. Overheating; Boiling Coolant

Kawasaki KLX300 owners report that their bikes overheat when pushed hard in scorching climates if not tuned or maintained correctly. Overheating can damage the engine and transmission, causing the coolant to overflow.

“04 KLX300… I took the bike out of my backyard to the trails up the street for the first time yesterday afternoon with the kids for a “real ride,” riding 1st or 2nd gear very slow for about 7 miles, and I noticed that it was overheating, boiling [coolant] out the overflow tank after about 6 miles. I took it home right after I let it cool off and checked the plug to see if it was running lean, but the plug looked perfect. Is this overheating normal? Is there something I should check out? Is there something I can do to prevent this from happening next time out?”

“Before I sold my 2001 KLX, it overheated. I could hear it boiling in the radiator on Utah rides (50 and sometimes 80-mile days) in hot weather. My radiator sounded like a freaking teapot. I fixed the issue by going to an 80/20 Antifreeze and water mix. Remember, pre-mix antifreeze is 50/50 – that is NOT good enough.”

“Had my KLX 300 for almost a year. Love it, but overheats when riding hard.”

Some common causes of Kawasaki KLX300 overheating are as follows:

• Lean jetting: Adjust the carburetor jets or fuel screws to enrich the air/fuel mixture and lower the engine temperature.
• Faulty cooling system: Check and replace any damaged or clogged parts, such as the radiator cap, fan, water pump, or thermostat, to improve the coolant circulation and cooling efficiency.
• Improper coolant level: inspect and maintain the coolant level between the low and high marks on the reservoir and inspect and seal any leaks.

2. Unbalanced Suspension

The KLX300’s suspension is adjustable to perform on various terrains. That said, owners of older year models complain that the rear and front suspensions are unbalanced, as they’re set up for different-sized riders.

An unstable suspension can affect the handling, performance, and safety of you and your KLX.

“You will need suspension work. The [Kawasaki KLX300] bike comes unbalanced. Forks are set up for a 155 lb. rider, and the rear is for 185.”

“I switched from stock 5-weight fork oil to 7.5, and it seemed to balance the suspension. I also ground the shifting star myself with no problems.”

Some of the common causes and solutions for unbalanced suspension are:

• Stock springs: Replace the stock springs with stiffer ones in the front and softer ones in the rear, to balance the bike and improve stability.
• Improper sag: Adjust the preload on the fork or shock, to set the sag at around 33% of the total travel, to optimize the geometry and steering.
• Incorrect damping: Adjust the compression and rebound clickers on the fork or shock to fine-tune the suspension response, to match the spring rate and riding conditions.

3. Mismatched Valve Shims

Another common problem with the Kawasaki KLX300 is uneven valve shim wear, resulting in poor valve timing.

The KLX300’s four-stroke engine has four valves, which require periodic adjustments to maintain optimal performance and reliability.

The valves are adjusted automatically by shims, thin metal discs that fit between the valve stem and the lifter.

The shims’ thickness affects the valve clearance.  

Mismatched valve shims can cause the valves to be too tight or loose, affecting the engine power, compression, noise, or starting.

“The OEM valves are suspect as well. Some options work, and if you go to the source, you will get a better price.”

“The intakes and exhausts will erode, cup, and go out of adjustment quickly. SS replacements will last a few seasons; I used to manufacture these items for stroker.”

Your Kawk’s valves can wear out over time due to friction, heat, or dirt, which can change the valve clearance and require new shims.

Valve wear can be prevented by using good-quality oil and filters and checking the valve clearance regularly.

4. Wrong Wiring Diagram in Manual

Owners of the DS edition KLR300 claim that their owner’s manual came with the wiring diagram for the KLR300R, which doesn’t match the DS’s specs.

This can confuse when conducting electrical repairs like changing fuses, swapping stators, or installing after-market parts.

“It is for the 300R. For some reason, Kawasaki does not have the wiring diagram in the DS model manual. I had and worked on the late 90’s era KDX200/KLX300, and they shared the same wiring harness, most bikes similar in size also do. Many parts for a small model Ninja fit the KLX230, like levers. It should be close enough to figure it out; shame on Kawasaki for not having it in the manual.”

5. Only Idles with Choke On

One frustrating issue sometimes reported by KLX300 owners is when the bike only idles with the choke on, which means that there is too much air and not enough fuel in the mixture.

The KLX300 has a carburetor that mixes air and fuel for the engine, but it can idle poorly if it is dirty or leaky.

If your Kawasaki KLX300 only idles with the choke on, the cause could be dirty pilot jets, a vacuum leak, or bad fuel.

Restore your Kawasaki’s idle function by cleaning the jet, sealing the leak, or replacing the fuel.

6. Starter Switch Shorts Out Easily; KLX300 Won’t Turn Over

The newer KLX300 year models have an electric start system that uses an electric starter switch to turn the bike on. Owners report that this electric starter switch sometimes fails due to corrosion and that their KLX develops hard starts.

“I just bought a brand new 2021 Kawasaki KLX 300. I really like the bike; I ride it almost every day on the road and off-road. But it’s had a couple of issues in the short amount of time I’ve had it (about a month and a half). The electric start button stopped working efficiently one day after rough trail riding. I brought it to the dealership, and they said the button itself is defective, and I have an appointment for them to replace it under warranty; it is no big deal; I can still start the bike. It just takes two or three pushes of the button.”

Some of the common causes and solutions for starter switch shorts out easily are:

• Dirty or corroded contacts: Clean the metal contacts on the switch with contact cleaner or sandpaper, and apply dielectric grease to prevent corrosion.
• Loose or broken wires: Tighten or repair the wires that connect the switch to the battery, the starter motor, and the ignition system with electrical tape or solder.
• Faulty starter relay: Test and replace the starter relay that amplifies the current from the battery to the starter motor with a multimeter or a jumper wire.

7. Slips Into Neutral from Second Gear

Kawasaki KLX 300 riders have reported that their bike’s transmission experiences false neutrals, particularly in second gear. False neutral is when your the gearbox slips into neutral without your input, catching you off guard and disengaging your engine.

“I’m having a problem shifting into second. Most of the time, when I’m out on trails and I want to shift from first to second, the gear shift won’t grab second and jump down into neutral. Sometimes it will do these two or three times in a row. I’ve started keeping up the pressure on the shifter until I’ve released the clutch, and that seems to work, but I feel like a new bike should not be doing this. This is not me shifting improperly. It’s something strange going on.”

Some riders resort to adjusting their shift star in a metal fabrication machine. Others purchase an upgraded shifter from the dealership or an aftermarket manufacturer.

“[Is there a] website of a gear manufacturer that addresses the slippage problems that KLX300s are known for?”

“Are you talking about false neutrals? Sometimes this happens when shifting from 1st to 2nd or downshifting from 2nd to 1st. You get into neutral at the worst time. If this is what you’re talking about? I have a fix for that…  [Install] a modified shift star and stainless-steel spring sleeve. My machinist … has it programmed into his milling machine. It takes about 5 minutes to cut. They take the false neutrals away. More positive shifting.”

“I second that; well worth the money. I noticed an immediate difference on my ’07, so it’s something Kawasaki never addressed over the years.”

8. Idler Gear Problems

The idler gear is a small but essential part of the KLX300 engine’s kickstart system. The KLX300 has both an electric start and a kick start. The idler gear helps to transfer the kickstart force to the engine. In some cases, the idler gear comes from the factory unaligned. It can also wear out or break over time.

“I found that my gear was also out of “mesh” alignment with the other two gears due to side-2-side play, and I shimmed it to align them better. I didn’t think about the bushing being out of center-line with the gear. That just seems like bad engineering. My thought was that if the bushing were actually wider and a bit thicker, you would be able to get a snug but workable fit that would limit the deflection of the gear and therefore reduce pressure and wear on the bushing. This would (hopefully) make the gear last much longer and survive occasional bad starting practices.”

The electric start makes starting the bike easy and reliable, especially in cold or high-altitude conditions.

The kick-start system is a backup option if the battery is low or dead.

Idler gear problems can stem from hard kickstarts, but many riders report their kicker fails due to poor factory gear alignment or inadequate engineering.

If the alignment is bad enough to cause grinding, metal shavings can enter the oil or transmission.

I bought an ’06 in April of ’06 [and had] over a year of good riding. I thought the Kickstarter felt a little different while kicking, and then in June ’07, I kicked it over, and it made a crunching noise, and the lever [detached and]  just stayed down on the ground. I have an extended warranty, so I brought it back to the dealer. They replaced the starter gear but did not split the case even though I told them friends recommended it. I rode it a couple of miles, and the broken pieces worked up into the engine, and it ground to a big old halt! Back in the shop again

To prevent or fix idler gear problems, you should inspect the gear regularly, kickstart the bike gently and smoothly, and consider replacing the gear with a newer, modified version.

What Are the Pros and Cons of the Kawasaki KLX300?

Pros:

• Smooth, counterbalanced engine
• Adjustable suspension front and rear
• Long-travel suspension that can handle various terrains and conditions.
• Six-speed transmission that delivers smooth and versatile performance.
• Reliable and durable engine and transmission
• Competitively priced dual sport machine
• Flexible and fun power delivery
• Small and easily manageable on the trail

Cons:

• Seat height might be challenging for shorter riders.
• Outdated design and looks.
• Heavier than some competitors
• Non-adjustable front brake lever
• No fuel gauge or tachometer
• Suspension may be too soft for aggressive riding or heavier riders.
• May need frequent valve adjustments.

What Do The Reviews Say?

“The KLX300 is a capable and enjoyable dual sport that delivers smooth and consistent performance on any surface. It has a powerful and torquey engine that can cruise at highway speeds or rip through the dirt and a durable and adjustable suspension that can absorb bumps and jumps. The bike is also easy to ride and control, with a low seat height, a lightweight, and a simple layout. The KLX300 is a bike that will satisfy your adventurous spirit.” – Cycle World.

“The KLX300 is a great bike for anyone looking for an easy-to-ride dual sport that can handle a variety of terrain. It has enough power to keep up with traffic and climb hills, but not so much that it will intimidate new riders. The suspension is plush and adjustable, and the brakes are strong and smooth. The bike is also very fuel-efficient and low-maintenance, making it a practical and economical choice.” – Cycle News.

What Are Some Alternative Models?

Related: 7 Common Problems with the KTM 390 Adventure (Explained)

What’s the Resale Value of a KLX300?

Sources:

Kawasaki Klx 300 Motorcycles for Sale Near Me – Cycle Trader

2022 Kawasaki KLX300 | Cycle World

2021 Kawasaki KLX300 and KLX300SM Review – Cycle News