6 Most Common Kawasaki KX 250 Problems (Explained)

The Kawasaki KX 250 is a perennial favorite in the 250cc dirt bike category.

The engine pulls well in the mid and high ranges, and its neutral chassis offers ergonomics to suit a wide range of riders.

And with recent suspension upgrades, color modifications, and bodywork, the KX 250 is more appealing than ever.

In this article, we’ll take a closer look at its most common problems…

1. Vacuum Leaks in the Air Intake Manifold

Riders of Kawasaki KX 250s from the early 2000’s sometimes report problems with their motorcycle’s idle staying high after revving, failing to rev back down to idle. High idle revs on a KX 250 indicate a vacuum leak in the air intake system.

One of the earliest signs is the erratic idling, even when the choke is pulled and the KX 250 is warming up.

Here’s how a real-life Kawasaki KX 250 owner described the strange shifts in idling:

“I start the bike up on choke, it idles very high (expected), then after about 30 secs I push the choke back in, it idles for a few seconds then goes to stall, I pull the choke back out for a couple of seconds then pus it in wait for it to stall and repeat the process until it idles for more than a couple of seconds, even when fully warmed up it will stall if you allow it to be idle for more than ten or so seconds. Also, if I open the throttle and build the revs higher when I let the throttle, it will not drop back to a low idle; it will idle very high.”

Additionally, suppose the air filter or intake of your KX dirt bike is corroded, damaged, or punctured enough to cause an air leak. In that case, you’ll hear the popping and banging noises during deceleration.

This is because the damage to your air intake lets too much air into your carburetor, causing your fuel mix to run lean on fuel.

• While many of the Kawasaki KX 250-year models manufactured in the early 2000s were known for overheating, the lean air:fuel mix causes the dirt bike’s 249cc engine to run significantly hotter than usual.
• You’ll be able to detect the lean fuel mixture, indicating the presence of extra air in your lines, by checking your spark plug.
• If it’s white, there’s likely a vacuum leak somewhere in your KX 250s air intake manifold. 

We’re unsure if this common issue with the early 2000s Kawasaki KX 250s is due to a flaw in the intake, improper upkeep, or just because many of these bikes are 19+ years old and have been passed down from owner to owner on the used market.

2. Valves Go Out Of Adjustment, Causing Compression and Fuel Leaks

One common issue reported with the Kawasaki KX 250 is valves frequently going out of adjustment. Once too tight, the valves fail to open correctly, causing a compression leak that can push fuel out of the drain tube below the bike. 

• If your valves are out of adjustment, the drop in compression will be significantly detectable while kickstarting the dirt bike, as there will be less resistance and the cycle will kick start much easier than usual.
• If you suspect the compression is weaker than spec and consider yourself a decent home mechanic, you can buy the tools needed to run a compression test by following the instructions online or in the Kawasaki dirt bike’s owner’s manual.
• If you’re unsure of the process, a Kawasaki-trained mechanic can run a compression test in no time and conduct a full inspection of your valves to ensure they’re adjusted to spec and aren’t worn.
• Worn valves will need to be replaced immediately, as they will continue to seat improperly even after they’ve been adjusted.

However, if the valves are adjusted to spec, we suggest you refrain from tampering with them, mainly if you’re on a carbureted KX 250, as the carburetor float needle could be worn.

A worn or jammed carburetor can manifest similar symptoms to an improperly seated valve.

3. Outer Intake Valve Springs May Break

In recent years, a more serious common problem on the Kawasaki KX 250 was broken valve springs. In some consumer reports published online, KX 250 owners claim the situation can be severe enough to cause a total engine failure.

Kawasaki responded to the reports by issuing a bulletin to prompt customers to bring their KX 250s in for a free outer intake valve spring replacement.

The bulletin claimed that the springs were breaking due to the improper shaping of the coil at the tapered end of the valve spring.

• For riders who use their KX 250 dirt bike for light rips around the neighborhood dirt track, the problem may manifest as trivially as extra resistance when starting the bike while it’s hot.
• Riders who race their KX 250  aggressively around sports tracks or rev high for stunt riding say the problem can be severe enough to cause their engine to explode after less than 20 hours of use.
• The problem was worsened by the higher compression piston ratings the 2020 year models were fitted with.

Suppose you suspect your Kawasaki KX 250 suffers from symptoms that indicate a failing outer intake valve spring. In that case, we suggest you take it in for a free replacement before riding it any further, regardless of how trivial the symptoms are. 

4. Clutch Plates Might Explode Through the Motor

One frequent problem on the 2021-year model Kawasaki KX 250 dirt bike is a faulty clutch diaphragm spring that isn’t strong enough to support the clutch plates. The clutch plates slip during operation, which causes friction and overheating until the spring has enough kinetic energy to dislodge.

Some online reports claim that the plates need to be replaced after less than 10 hours of riding to keep them from overheating and breaking from the friction.

More durable aftermarket clutch plates are available that will last longer than the stock 2021 plates Kawasaki installs at the factory.

That said since the problem’s core is inadequate integrity in the clutch spring itself, even the most durable clutch plates will slip and fail while operating, causing overheating.

These replacement clutch plates may last for more engine hours, but no clutch plate can endure the friction caused by a slipping spring for long.

• One Kawasaki technician we heard suggested replacing the clutch with the setup from the 2020 year model KX 250, as it fits seamlessly into the 2021 gearbox.
• That said, strictly replacing the clutch plates is not a long-term solution.
• The faulty clutch diaphragm spring on the 2021 models will also destroy the 2020 clutch plates.
• Therefore, Kawasaki technicians suggest that owners of 2021 KX 250s replace their inner clutch hub, pressure plate, and all five clutch springs, completely removing the 2021 clutch setup to ensure the new plates won’t slip.

Other reports claim that Kawasaki technicians solve the problem by installing an upgraded housing component on the right side that sends more oil to the clutch.

The reports claims the upgrade is free at Kawasaki dealerships once it’s been determined that your clutch is overheating. 

Note: The Kawasaki KX 250 uses a hydraulic clutch which requires clean fluid in the clutch lines for proper functioning. If the fluid is low or air gets into the system, the clutch components overheat and expand, which can cause the clutch to slip on any year model. The issue described in this section pertains to the weak springs on the 2021 year models and can happen regardless of hydraulic fluid lives and routine owner upkeep.

5. Water Pump Failure (2021 Models)

The 2021 year model Kawasaki KX 250 was known to have a water pump problem preventing coolant from circulating properly through the engine, which could cause engine overheating and boiling coolant to vaporize and steam from the coolant reservoir.

While overheating can be expected on dirt bikes ridden hard through thick mud for hours under the hot sun, the KX 250 equips a liquid cooling system that cools the bike’s sealed engine by flushing it with cold fluid to keep it at a safe operating temperature even when it’s sweltering outside.

The water pump is responsible for keeping that coolant flowing to the engine from the radiator.

The frequent water pump failures on the 2021 resulted in blown seals, coolant leaking from the clutch cover, coolant leaking into the oil reservoir, vaporizing coolant, and engine overheating leading to starting problems and engine stall outs.

6. Carburetor Flooded with Fuel

One of the most common problems affecting used models of older year Kawasaki KX 250 dirt bikes is fuel leaks and starting problems resulting from a flooded carburetor. Flooding is when the carburetor bowl overflows with fuel, either due to a fuel clog or an improperly seated float needle.

The KX 250 was launched in 1974, and up until 2013, every version of it has been carburated.

On the carburated year model KX 250s, the needle valve is set to a spec position that stops the bowl from filling with fuel after it reaches the ideal level.

If the needle is set incorrectly, the bowl will overfill and flood.

The excess fuel drains down the carb and floats into the engine, causing stall outs and issues with the bike starting.

If the needle is simply out of adjustment, resetting it will be enough to stop the carburetor from flooding.

If the fuel overflow is caused by a damaged or worn needle or a fuel clog, the carb must be uninstalled, disassembled, and cleaned out to restore the fuel level to its idle setting.  

Pros and Cons

Pros 

• Reasonably Priced Compared to the Competition.
• Sturdy and Dependable Overall
• Outstanding Cornering and handling
• Effective Stopping Power
• Nimble Chassis
• Simple, Meat-and-Potatoes Dirt Bike Concept
• Looks Tough and Stylish.
• Fun to Ride 

Cons

• Lower Fuel Economy than most bikes in its class.
• Frequent Valve Adjustments make it High Maintenance.
• Outer Air Valve Springs Might Break
• Vacuum Leaks in the Air Intake can cause Air or Fuel Leaks
• Clutch Plates Break Easily (2021 Models)

What Do the Reviews Say?

“The KX 250 engine has a crisp throttle response and a linear powerband. The low-end power is average, making it essential to downshift before entering corners to avoid slipping the clutch excessively to get into the midrange. Once there, the engine pulls well and has decent top-end power.”

“The [KX 250] has a raspy note to it, especially in the higher rpm. A harder-hitting, more powerful engine would make it more fun to ride and better suited for higher-level riders. Overall, the predictability of the KX 250’s powerband makes it user-friendly and easy to ride effectively for riders of most skill levels.”

“The KX250 uses a Showa Separate Function Fork (SFF) and Showa shock. The fork is stiff with the stock clicker settings and feels harsh when braking bumps are hit. It became much plusher in the beginning of the stroke after we decreased the spring preload and softened the compression.”

“The KX250 corners well and is stable at speed.

“The bike as a whole feels relatively small, especially in comparison to its competitors, which can be a good quality as it makes the KX250 feel even lighter and easier to put where you want it. “

SOURCE: 2019 Kawasaki KX250 First Ride Review | Dirt Rider

What’s the Resale Value of a Kawasaki KX 250?

What are Some Alternatives to the Kawasaki KX 250? 

Related: 5 Most Common Problems With Yamaha YZ 250F (Explained)

Sources:

2019 Kawasaki KX250 First Ride Review | Dirt Rider

Bad Water Pump Symptoms on a Dirt Bike or ATV | MotoSport

Dirt Bike Carburetor Troubleshooting Guide On 5 Regular Problems (gearhonest.com)