The Best KLX250s Modifications

The Kawasaki KLX250s is a versatile combination of playbike and full-on trail burner. Right out of the box, the KLX is a willing companion, both on the dirt and on ice! It is an un-intimidating ride with a well-balanced chassis and handling. But, like many bikes, a few accessories and upgrades go a long way to improve an already good machine.

Most of the parts I installed are available from Twisted Throttle. If you decide to buy any of the items I mention in this article, please buy them from Twisted by clicking on the links on this page. That way, I get a small affiliate payment that helps me continue to write and share helpful articles like this. Thanks.

Bike Protection

Falling down is often a part of off-road riding, so it makes sense to protect the bike from damage. It’s bad enough to bend a lever or handlebar, but it’s worse if the damage strands you out in the Boonies.

Radiator Guards

Here is a part that is vulnerable to damage and expen$ive to repalce. Kawasaki thinks that the plastic fins are good enough to thwart an attack by a roosted rock or an errant stick or keep a radiator from being smashed in a fall, but they aren’t…trust me. I toasted a radiator on a KDX200 many years ago during a routine tipover and learned my lesson.

Skidplate

SW-MOTECH also made the skidplate that I installed to replace the OEM plate. The SW plate is made from a 4mm-thick aluminum base plate and 3mm-thick side plates. I’ve whacked some seriously solid rocks with this plate with no consequences whatsoever (see photo).

Barkbusters Handguards

Handguards should be at the top of the list for things to install. Not only do they protect your vulnerable metacarpals, but they also keep your levers from bending or breaking when you fall or rap a tree.

The Barkbusters are the original handguards and come with various shaped plastics. The VPS plastics with upper wings provide good wind and brush protection without being too large.

Handlebar

Yes, the KLX comes with a handlebar. But, it’s a P-O-S. It will bend the first time you tipover…guaranteed. The ProTaper bar I installed has taken two significant hits and they are still like new. There are many bends to choose from, but the Henry/Reed bend is just right for me.

Dual Sport Grips

Dual sport grips provide a balance between comfort and grip for all-day control. These grips lack the ridges that are found on most off-road grips (including the stockers). Even though they aren’t as secure, I like the comfort these provide (See photo and link).

Folding Mirror

The stock mirrors are easily damaged in a tipover, so you may as well put them away now and buy an inexpensive folding mirror that can be tucked away when you don’t need it and extended when you have to do some pavement riding to get to the next trailhead.

Tires

My tires of choice for both off and on-road are Pirelli MT-21s (front) and the Dunlop 606 (rear). They aren’t the best off-road tires but are full knobbies.  They aren’t really made for much pavement riding, but offer a great (90% -off road/10%- on road) balance.

The Ice Tires I use are Fredette Canadians. These are the best combination of grip and slip so you actually learn about traction management…as opposed to the Marcel tires which grip so hard that you can throw the bike in without a care. (aka, Cheater tires)

Big Bore Kit

OK. As great as the stock KLX is, it became apparent that it could use more power when it struggled to ascend a particularly steep and rocky trail at Hatfield McCoy. The power challenge became even more of a hindrance when I started riding on ice where the vast expanse of frozen water begged for maximum drive. While I had a boatload of fun on the rock hard ponds and lakes with the stock motor churning out every bit of its 17hp, I decided to install a 351cc big bore kit from Blue Bill.

The reasonably priced $535.00 kit includes a new re-bored cylinder, piston, rings, wrist pin, and gaskets. Of course, I could have sold the KLX and bought a bike with more displacement, but that would have certainly cost a lot more money. Besides, I like the KLX’s character, so I went for it.

Horsepower and torque increase is modest at somewhere in the 5hp and 6 ft lb range, but that is a 30% and 40% increase from stock (I suck at math, but that’s close enough). The result was noticeable once I went through a short break-in period and was able to open it up. I can now whack the throttle open and the bike responds briskly.

The Build

Installing a big bore kit isn’t very difficult, but it takes some mechanical inclination that consists of more than remembering “lefty loosey, righty tighty”. I’ve done my share of moto-surgery, so I knew what I was getting into. Still, it’s unnerving to remove the head, camshafts, cam chain, cylinder and piston ,and then get it all back together again without any important parts leftover.

I disassembled the bike following the Kawi shop manual and all went well. I removed all the leftover gasket goop from the case with an oiled Scotchbright pad and was ready for my friends Adam and Jay to show up and give me re-assembly help. After 4 hours or so in a cold garage, the motor fired up and sounded good. I was scheduled to ride the next day on the ice in New Hampshire, so I would soon know if we did things right.

Jetting and Exhaust

Some jetting was needed to manage the extra displacement. I added two washers underneath the needle clip to raise it and replaced the 118 main jet with a 125 and changed the slow jet from a 35 to a 38. The air screw is turned out 2.5 turns (you have to drill out the EPA plug the get jet access). That combination worked great right out of the box using the stock exhaust.

That’s right, I’m sticking with the stock exhaust for now. I value a very quiet bike, especially when riding off road. Yes, the heavy stock can and header pipe is certainly holding back the power potential, but I’m okay with that for now. I’m told the hot setup that is also reasonably quiet is the FMF power bomb header pipe in combination with the FMF Q4 muffler.

Verdict

I made sure to warm the bike thoroughly in the 10F temperatures before taking the bike for its maiden voyage on Hoit Pond. It felt good, but the instructions were to keep it at below half throttle for 100 miles before going WFO. Using conservative throttle, I immediately felt the increase in torque, but not much in the hp department. That would come later.

I managed 4 sessions (about 40 miles) at no more than half throttle before I slowly began opening it up to break it in the way racers do: hard. It ran great and pulled strong. I was pleased. The additional power meant I could use different techniques for getting the bike turned; namely whacking the throttle mid corner. This would hook the bike up nicely to finish the corners. The old motor couldn’t manage this feat. Cool beans.

Why a KLX?

My previous off-road bike was a 2000 DRz-400e. The DRz was a great bike; it had lots of rear tire spinning, wheelie-inducing power, but was a beast, especially in tighter trails. I now know the benefits of a more docile bike with a lower seat height and civilized manners. The KLX is a great platform that just needs a bit of love.

The bike protection goodies are a must-do if you don’t want to damage vulnerable parts and possibly become stranded in the middle of the woods. And the Barkbusters are critical to protect your hands and levers. The stock handlebar will likely bend if you look at it wrong and the mirrors will break if you scream too loud. So, get those things taken care of ASAP.

As far as the power upgrade goes, I think it is a worthwhile way to spend some money. The stock motor is reliable, but barely adequate when the going gets tough. It’s a great motor for any around town riding and level off roading. If you are a fast off road rider you won’t be looking at a KLX, so no need to compare this bike with a KTM or CRF-X.

No, this is for the person who rides both on and off road and wants a bike that is easy to ride and instills confidence. This bike is still too tall for a lot of riders, but is perfect for most middle to light weight folks of average height.

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