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What Are The Best KLX 140 Mods That Actually Make It Better?

Looking to get more power out of your KLX 140? Maybe you just want to upgrade the suspension to make it more comfortable so that you don’t get bucked off while riding? Whatever it is, I’m going to show you the best KLX 140 mods to make it faster and safer so that you have more fun and don’t get hurt!

In this article, I’m going to show you the cheapest and most practical mods, the best performance upgrades, why some mods work better than others, and how to get the most performance out of each modification or aftermarket parts. 

How to get more power out of your KLX 140

A stock KLX 140 has about 12 HP, which is enough power for almost anyone to ride and have fun, but more power is better, right?

The best KLX140 mods will give you more confidence to ride faster and safer
The KLX 140 is a capable machine, especially if you set it up for your style of riding

To get more horsepower and torque, you have to modify one of the following:

  • Airbox
  • Intake
  • Carburetor
  • Engine
  • Exhaust

Upgrading or tuning certain parts in one of those systems can help (or hurt) the power, but you need to figure out what kind of power you want first. There’s a difference between torque and horsepower, and it’s important to know what you want. 

When I say low-end torque, I’m talking about the power at low to midrange RPM. More torque means it will be able to accelerate faster at lower RPMs, and is generally easier to ride because it has a wider and smoother power curve. 

Horsepower generally refers to peak power at high RPM. This is great for acceleration and top speed, but adding more HP usually means that the engine has a narrow power curve. This makes it hard to ride because it’s “snappy” and hard to keep it in the “meat” or the power. 

Before you make it faster

Going faster can be a lot more fun, but not when you’re getting bucked around. You need to have your bike set up for your weight and riding still or else it’s just going to be more dangerous when you increase the power of your KLX140. 

Airbox mod

Does your KLX 140 have a lid on the air box? If yes, you can open it up by drilling some holes for more potential power. 

The stock air box is sealed up pretty well, which means the engine is better protected from dust and dirt getting through the air filter and into the engine, causing damage. But, this also limits the amount of air that can get to the carburetor. 

By opening up the air box, more air will get in, and more air means the engine can make more power. But that’s only if it’s jetted properly. If you’re concerned about dirt getting into the airbox, you can add some air vent filters (Amazon)

Jetting

Speaking of jetting, tuning your KLX 140 carb jets is one of the easiest ways to get more performance. Not only can you get more power, but your dirt bike can start and run much better, making it smoother and easier to ride. 

The stock jetting is pretty lean from the factory, so it’s hard to start and doesn’t run very smoothly, depending on your climate. Going from a 38 pilot jet to a size 40 pilot should help it start more easily, especially when cold. 

Replacing the stock 95 main jet with a 100 or 105 should also help smooth out the power and give it a slight bump in power. 

If you have done air box or exhaust mods, you’ll need to go richer (bigger), or else the air-fuel mixture will be too lean and it will run worse.  

Adjusting the fuel screw?

The stock fuel screw is not adjustable – at least not with a regular tool. Why is this important? Because the fuel screw tunes the pilot jet circuit, which affects starting and roughly 0-¼ turn throttle position, which is where most people spend most of the time riding. 

So, you can either buy a special D-shaped screwdriver that fits the fuel screw head or use some sort of grinder tool and hack away a slot so that a flat blade screwdriver fits. 

Carb mod?

Maybe you’re tired of dealing with the stock carb altogether, or have seen enough frustration from other KLX140 owners and simply want a better-performing carb right away. 

A common mod is converting to a KX65 carb, which is a Mikuni VM24 (Amazon) – I say “convert” because it’s not a simple “bolt-on” upgrade. 

You’ll need a custom intake boot to make it fit (more info on this TT thread), and then some jet tuning will most likely be necessary. A ballpark starting point is 20 pilot jet and a 120 main jet with the VM24. With some fabrication and tuning, you’ll have an easier starting, better running, and more powerful bike. 

Suspension upgrade

The stock suspension on the KLX140 is good… if you’re a beginner that weighs under 150lbs. But it also depends on which model you get. 

With that said, if you’re a heavier rider or you just want something that won’t bottom out as easily because you’re riding faster than the bike was intended for, there are some ways to improve the forks and shock. 

Stock forks

The stock forks are like most conventional forks on a trail bike – nice and plush with very basic damping. This means that it absorbs bumps and obstacles well at low speeds, but it’s like a pogo-stick when you pick up the pace. 

Cheap fork upgrade 

On a budget but willing to spend a few hours to get a better performing front end? Going to some stiffer springs (Amazon) will make a big difference if you’re over 130 lbs or ride aggressively. 

CRF250F BBR Fork Springs What Are The Best KLX 140 Mods That Actually Make It Better?

If it’s too stiff using two heavy duty fork springs, you can use one stock and one stiffer to meet in the middle for the overall spring rate. 
BBR part # for KLX140L heavy duty fork springs is: 650-KLX-1405
BBR part # for KLX140G heavy duty fork springs is: 650-KLX-1505

Next, you can use heavier weight fork oil. This will slow down the compression and rebound damping.

Raising the fork’s oil height will also help reduce bottoming. This reduces the air gap, making it harder to compress as the forks go down in the stroke. 

Rear shock

The stock rear shock actually has some adjustments that you can make easily and for free. You can adjust the sag (ride height), which you need to do anyway to get the suspension balanced. 

You also have some compression and rebound damping adjustment with the shock, which gives you more tunability to get better comfort. A stiffer shock spring (Amazon) will help if you’re heavy or constantly bottoming out the rear shock.
BBR part # for KLX140L/KLX140G shock spring: 660-HCR-8005

Gearing swap

The stock gearing on the Kawasaki 140 is actually pretty tall compared to its competition, such as the TTR125. Simply put, first gear is higher, so you can’t ride quite as slow. It’s not quite the same as 2nd on the Yamaha, but it’s close – more like a 1.5 gear for speed. 

You can do a quick sprocket swap to get more acceleration by going to a smaller front sprocket (Amazon) or a bigger rear sprocket. Or, if you have more power and want to take advantage of the extra torque to be able to short-shift, you can go bigger on the front/smaller on the rear for wider gearing and more top speed. 

Best KLX 140 exhaust upgrade?

I actually like the stock exhaust because it’s nice and quiet with decent performance. But, if you want some better throttle response, more horsepower, and a nicer look, an aftermarket exhaust is an easy choice because you don’t have to go inside the engine to change anything. 

The best exhaust upgrades for your KLX 140 are:

  • Stock exhaust mod – Remove muffler baffle for better throttle response but more noise
  • FMF Powercore 4 – Slip-on (muffler only) for better/more sound and slightly more power
  • Yoshimura RS9 system – Full system with better sound, power, less weight, spark arrestor, and quiet insert included (best overall system without being obnoxious)
  • Big Gun Evo – Full system with more power, noise, less weight, and a removable spark arrestor screen (great budget full system but loud)
  • Pro Circuit T4 – Full system with more power, noise, less weight, and a spark arrestor screen (best budget full system but loud)
  • Pro Circuit T6 – Full system with more power, less weight, more packing for slightly less noise, and a removable spark arrestor screen (great full system that looks good and is a little quieter than the PC T4)

To get the most out of your exhaust upgrade

Changing the exhaust, whether it’s stock or aftermarket, will change the air-fuel mixture because more exhaust is being pulled through the engine. This means that you’re going to have to adjust the carb jetting if you want the most power.

For example, if your bike is stock and the jetting is perfect for your climate, but then you put a Yoshimura exhaust system on it. It’s going to run leaner and it might actually have LESS power at certain RPMs – the opposite of what you might think is happening because it sounds faster.

So, you need to re-jet some or all of the jet circuits if you want it to:

  • Start easily
  • Have more power
  • Run smoothly – a poorly jetted dirt bike carb makes it erratic and hard/frustrating to ride
  • Be more reliable
  • Last longer

Big bore kit?

The easiest way to get more power is by going with a bigger engine, and you can do that with a simple and affordable big bore kit. The most common KLX 140 big bore kit punches it out to 170cc.

It comes complete with a cylinder, piston kit, and gaskets. If you can rebuild the stock top-end on your dirt bike, then you can install this kit.

You can expect to get more power throughout the entire RPM range, but mostly in the low-end and midrange for better torque if you don’t upgrade anything else on your bike – more on this in a minute…

As for reliability, it will last just about as long as a stock engine. Yes, more power means more heat and less life, but it also means you don’t have to rev it as high to go the same speed. This means you can ride at a lower RPM, making it just as, if not more reliable than stock!

I also recommend replacing the camshaft timing chain, especially if your engine has high hours. The timing chain gets stretched out over time, and the more it stretches, the more likely it will “let go” or allow a valve to hit the piston. This is even more important on a modified engine where you’ll likely be revving it higher – it’s simple insurance and doesn’t take much more time since you already have the engine apart.

Lightened flywheel?

If you simply enjoy modifying your bike for more power or performance, then the flywheel is something to consider. Most trail bikes have a heavy flywheel, which makes it easier to ride because it’s less likely to stall and smooths out the power. 

If you want to accelerate faster and have more “snap”, lightening your KLX140 flywheel will do just that. It doesn’t change the power, but it simply removes engine mass (weight), making it easier to spin. 

This gives you quicker acceleration, but it does make it just slightly easier to stall because there’s less weight to keep the engine spinning. This is a trade-off, which is why I don’t consider this a “beginner mod” for your Kawasaki 140 (or 150). 

Putting it all together for more power

Just doing one mod or mixing random parts together may not get the performance you expect. In fact, it could be worse in overall performance!

You need to start with a goal in mind, and then pick the mods that work best together to reach that goal. For example, if you want to boost the low-end torque, you don’t want to choose the biggest aftermarket carburetor and exhaust system that’s built for increasing top-end power.

Choose an exhaust that will give you a broad power band, tune the stock carb for that exhaust, and then adjust the gearing for the type of riding you’re doing. If that still isn’t enough power, then add a big bore kit and re-jet the carb for best performance and reliability.

What are the best mods for a KLX 140?

  • Airbox mod
  • Jetting 
  • Carb upgrade
  • Forks
  • Shock
  • Gearing
  • Exhaust
  • Big bore kit
  • Lightened flywheel

What’s the best mod to ride faster & safer?

You can do all of the mods I listed in this article, but there’s one mod that will give you the most speed and confidence. It can also be used on any bike you use for the rest of your life.

If you’re a beginner or novice rider that wants to quickly build your confidence, I want to show you how “upgrading” the rider (YOU!) will make the biggest and quickest difference in your riding. Click here to watch my free workshop!