Honda XR200R Mods Part 2 – Weight Reduction

Honda XR’s aren’t known for being high-performance dirt bikes. That’s a given… In stock trim. If you read Part 1 on XR200 Mods, you will know that there are a lot of parts that you can replace for better performance, such as: suspension, intake, and exhaust. Part two we’ll look at the parts that can be removed or replaced for the purpose of reducing the bike’s overall weight. One of the reasons why the Honda XR200R is so popular for trail riding is its simplicity and low weight compared to other bigger four-stroke trail bikes.

Wait, hold on! Why in the world would I spend all this time, effort, and hard-earned money to put this ‘outdated’ dirt bike on a diet? That is a good question, but I will answer that with another question… Have you ridden one that is properly set-up? It won’t win you many bets in a drag race, but if the race is up and through the gnarliest of terrain, this bike will putt to the top with less effort, all the while having a grin on your face (not that riding any dirt bike shouldn’t do that anyway). It’s just a complete package of being a mid-sized bike that is easy to ride, requires little maintenance, and having engine characteristics that make it desirable while still being big enough for many larger riders with some simple mods. Not to mention the fair amount of weight that you can subtract off of the XR200 that just makes it even more fun to blaze through single track trails. As long as there’s oil in the engine and gas in the tank, there’s very little chance of these bikes breaking down. But enough praise of this simplistic and less than eye-pleasing dirt bike; let’s get to the point!

Depending on the year XR200, the curb weight (meaning wet with fluids and ready to ride) is about 230 pounds, or just under 220 without gas. Many people have tried to get that number below 200. While it is possible, it starts getting expensive the closer you get. Getting under 210 without gas is pretty easy if you have some mechanical abilities and motivation. The difference that 20 pounds makes will be like riding a new bike. If you think it’s flickable in stock form, wait till you start removing some major weight, especially the un-sprung mass! More on this later…

The XR200 engine is close to 60 pounds, which is almost one third of the total weight. There’s not much you can remove from it other than a few ounces from the flywheel while staying on a budget and keeping it reliable. Instead, we will have to look at all of the chassis and suspension components to shed the weight. In reality, you can remove weight off of or replace almost any part with something lighter, depending on how creative you can get and how much cash you want to spend. Lightweight parts comes at a price. If you want a completely aftermarket chassis and titanium nuts/bolts for your XR200, you could probably get under 190 pounds, but the cost per ounce saved will be much higher than the first 15 pounds.

Pictured Is Chuck's (with consent from TT) modified XR200
Pictured Is Chuck’s (with consent from TT) modified XR200

Sprung Weight

Sprung weight or mass is anything that is supported by the suspension. This includes the frame, engine, plastics, etc… These parts aren’t quite as critical as un-sprung parts when it comes to handling performance, but everything adds up (or subtracts if you’re taking weight off). Having a low center of gravity is also very important, and lowering the CG will make the handling characteristics feel like the bike is lighter. So, even if you can’t necessarily remove weight from a certain part, re-locating it to a lower spot (without being obtrusive, of course) on the bike can improve handling by making it “feel” like you removed weight because the bike doesn’t feel as top-heavy.

Yes, now it’s time for some numbers. Below is a list of parts that can be removed or replaced with lighter components along with their weight estimates in pounds and ounces…

  • Handlebars – Swapping to aluminum bars alone will save about 1 pound. It’s the highest part on the bike, so this is a very easy weight reduction mod. If you don’t like the stock bars anyway, this is a great time to pick out a handlebar with the right bend, sweep and width to suit you. Every rider is a little bit different, which is why there are so many bars available.
  • Snorkel cover – The top snorkel cover on the airbox is not needed unless you are riding through waterholes or in very sandy conditions. This is worth almost half a pound.
  • Muffler – The stock muffler is fairly heavy. An aftermarket silencer can save 1 to 2 pounds. Otherwise you can pull the stock baffle out of the muffler for close to the same reduction.
  • Case guards – The stock engine case guards aren’t very effective. If you don’t ride in rocky terrain, you can take them off for a 1.5 lb savings.
  • Kickstand – I don’t know of any aftermarket aluminum kickstands, but if you can weld one up, that could shave another 1 pound or so. Otherwise just take it off.
  • Steering stem – A mid 80s XR250R aluminum steering stem can be made to fit in addition to the inverted forks (see below) to replace the stock steel stem. This is worth about half of a pound.
  • Seat – Drilling out some holes in the seat base will take off some ounces. Everything adds up in the end…
  • Plastics – Trimming plastics can save a few ounces here and there. Besides, if you do it right, they can make the bike look better too.
  • Shifter – Switching to an aluminum shift lever can save several ounces. If you ride in rough terrain or tend to hit your shift lever on objects, you might want to consider sticking with a stock steel lever. This won’t make much difference as far as handling goes because it’s relatively low on the bike anyway.
  • Pegs – The stock steel pegs are heavy compared to aluminum ones. If you can find some cheap aluminum pegs off a Honda MX bike and adapt them, that can drop another pound or so.
  • Tabs – If you really want to get crazy, grinding off any unneeded tabs from the frame will save a few ounces here and there. Just remember that it will start to rust if you leave the metal bare. This is a good excuse to strip the whole frame down and get it re-painted or powder-coated to make it look like new.

Total Sprung Weight: 6 pounds

Un-sprung Weight

Removing any kind of weight is good, but if you can shed un-sprung weight, the results will yield significant results as far as handling and performance goes. Un-sprung mass is all of the suspension components, such as the forks, wheel assemblies, shock, swing-arm, linkage, etc. Removing weight from these parts is more effective than if you were to remove the same amount of weight from sprung mass because it is the rotating and moving with the ground surface and suspension.

Lightweight aluminum rims are highly sought after compared to steel rims because they can reduce a great percentage of rotating mass. A lighter wheel will be a light more responsive when going over obstacles and bumpy terrain because it doesn’t take as much force to move it. This allows for greater traction and improved handling. I don’t want to go too in-depth on this subject or else you’ll be sitting here all day. There’s no set equation that determines how much un-sprung weight removed that would equal the amount sprung weight. Just know that un-sprung mass has a greater effect on handling performance.

Now we’ll look at the key parts for removing weight from the suspension and wheels to make the XR200 the bike that Honda should have made…

  • Swing-arm – The stock swing-arm on XR200R’s are steel and can be swapped out for a XR250R aluminum swing-arm (’86-’89) with little modification. It’s about 3.3 lbs lighter and can be found on eBay for under $100. Look for one that still has everything on it if possible, such as the chain guide, slider, and axle adjusters.
  • Linkage – Another fairly easy weight savings is switching to an aluminum swing-arm linkage (1984-’85 XR250R). It’s just over 2 lbs lighter, but is debatable on being sprung or un-sprung mass. For less than 50 bucks, this is another good mod. However, the grease fittings may be broken off, and new bushings may be required.
  • Forks – The biggest fork mod for weight savings is switching to a CRF150R or CR85R front end (depending on what size front wheel you use). It’s about 6 lbs lighter, but is a little more work and costs several hundred depending on how hard you look. This is by far the most expensive mod on this list, but yields good results on both the weight and performance side of things. A servicing and re-valving will make this bike handle any trail you throw at it, especially if the rear suspension is dialed in as well.
  • Wheels – A late 80s RM125 rear wheel is a good 4.5 lbs lighter than the stock XR200 wheel. It can be modified with new spacers and some bearings that match the XR axle size. A complete wheel can be had for 100 bucks or less on eBay. Late 80s RM125 rear wheels are 18″, which is easier to find tires for. Many people swap over to 18″ XR250 rear wheels for the better traction you get from a bigger diameter tire. However, this will have some effect on gearing.
  • Sprocket – The rear sprocket is one of the easiest weight saving mods. The stock steel sprocket is about 1.7 lbs heavier than an aluminum sprocket. You can buy an aftermarket rear sprocket or certain bikes that have the same bolt pattern will work. Some examples are: mid to late 1980’s XR250, ’99 and newer YZ125, ’01+ WR/YZ250F, or ’01+ WR/YZ400/426/450F.
  • Tires – This depends on what size wheel you have and what kind of tire you want. The size that a tire shows may not be exact. Trials tires give good traction, but weigh more than standard off-road tires. If you want the lightest tire, go with something that’s narrow.

Total Un-Sprung Weight – 18 pounds

If you put all of these savings together (assuming you haven’t added any weight), you should meet the goal of having a sub-200 pound XR200R trail bike without gas! I could go on about every little part that you can replace or make a custom lightweight replacement for, but that’s when a simple and budget-minded project turns into a full-fledged hobby and pocket burner. Other than the CR/CRF front-end on the lists above, all of these parts or mods are relatively cheap and easy for a DIY person to do.

I can’t take all of the credit, as some of this information was from founded from members on ThumperTalk. If you have personally done additional modifications to make your XR200 lighter, please feel free to post your results or email me so I can add it to this article. This information, like all of the articles on Motocross Hideout, are for the benefit of other riders that want to learn more about their dirt bike and be able to work on it themselves.

-Tom Stark

How To Swap TTR125 Carb to VM24 – Video Tip

Having starting or running problems with your TTR125? There’s a good chance that the stock carburetor is your problem. Instead of spending hours trying to fiddle with it, a carb swap can save you a lot of headaches and make your bike start easier and run much cleaner. Here’s a step-by-step video tutorial on how to convert to the Mikuni VM24 carburetor. If you’re unsure about this conversion or have questions on why you should do it, read all the details on swapping out the stock carb HERE.

Honda XR200R Mods Part 1 – Performance

Is the Honda XR200 a race bike? No, but it is a reliable, torquey, lightweight, easy to ride, and simple trail bike that is great for tight and technical riding. It may not be the best at anything in stock form, but it does a lot of things very well in the off-road scene, and let me tell you, it is a BLAST to ride! The XR200R started out with decent suspension back in the 80s that was adjustable and fully rebuildable, but went downhill in the 90s until Honda stopped importing the bike to the U.S. in 2002.

The XR200R was featured as the Used Dirt Bike of the Month in July of 2013 here on Motocross Hideout. It briefly goes over the pros and cons of this bike, but now we will go over some real mods and tricks to make your current or future XR200 rig a force to be reckoned with.

It’s hard to find used ones in good shape, but with some TLC, along with a little bit of money thrown at it, you can be spinning laps through the woods in no time!

First thing to look at is the suspension. If you weigh over 150 pounds and are aggressive at all, the stock suspension on any year XR200 is under-sprung, as well as under-damped. 1981-83 had single adjustable shocks and 1984-1991 were fully adjustable. After that, Honda stuck on a cheap, non-rebuildable and non-adjustable rear shock, along with shorter forks. Both combine for a lower seat height and an even lower performing trail bike. While it may have the same power-plant throughout the years (except for the ’84/85 RFVC 4-valve engine), many people base the XR200’s capabilities off of the ’92 to ’02 because there are more of them to be had on the used market.

Rear Shock

The stock shock on an ’84-’91 (84-85 XR250 shocks are the same and will bolt on) are surprisingly good, and much better than the non-adjustable shocks on any of newer XR200’s after being rebuilt. They’re not too hard to find on eBay, but a lot of them are in rough shape. You will want to service it at the least. A new head seal kit is a good idea, and if you really want it to perform better you can send it out to get re-valve for your weight and riding style. This is the best bang for your buck, but if you want the highest performance, a Works shock will cost you a hefty 500 American buckaroos, give or take. While it’s a great upgrade compared to the 92-02 stock pogo-stick shock, it may not be worth it if you’re on a budget and don’t need a full-on race machine.

Front Forks

Much like the shock, the forks were downgraded on the Honda XR200R after 1991. They were not adjustable, and they lost some much needed suspension travel; thus lowering the seat height. This was done to make it more of a ‘beginner bike’. It’s not difficult to swap out the internals to bring the travel back up, but it’s just one more thing to do. The best forks from an XR200 are on the 1986-1991 models, and they can bolt right on to the later model 200’s. However, this isn’t the only option you have (more on this shortly).

'02 XR200R
’02 XR200R

If you get the early model XR200 forks, you can get stiffer progressive springs that can handle heavier and more aggressive riders and are fairly inexpensive. Servicing the forks and putting some heavier weight fork oil can help slow the damping down, which is probably the weakest point of any stock XR suspension component.

If you want to spend a little more time and money, you can swap out the stock forks from with a set from another bike that has better/bigger forks. 1984-85 Honda XR250R forks are bigger, but they require the complete front-end to fit on an XR200. If you go this route, you will also get a much needed front disk brake upgrade. They only have 10 inches of travel (same as the early XR200), but the internals are beefier so it can take more abuse.

A step up from that would be the forks from a 1986-1995 XR250R. They have 11 inches of travel and are 41mm in diameter, compared to the stock 36mm on the 200R. They have a disk brake as well and will require the complete front-end to work on the XR200. If you do this swap, the front end will be higher, causing a difference in bike geometry and the handling with change. To combat this you can pull the forks up in the triple clamps, or change the rear-end height with a different shock/linkage that will raise it up to level the bike back out.

Another common swap, and probably the best bang for the buck if you can find a cheap roller, is swapping a front-end off of a late 80s Honda CR125/250R motocross bike. They aren’t inverted forks like modern MX bikes, but they are cartridge forks that perform a lot better than the stock conventional damper-rod forks. They also have disk brakes that are leaps and bounds better than the XR brakes. These aren’t technically a ‘bolt-on’ swap, but a specific height for a spacer is the only major part you will need to ‘fabricate’. These forks will definitely raise the height of the front-end, so you’ll want to move the forks up and/or compensate with the rear suspension or else the handling will suffer.

Intake

I could go on for quite some time about suspension mods for this bike, but I’ll let you decide and continue the research if needed. I wanted to cover suspension mods first because “go-fast” mods won’t help much when you’re bottoming out on braking bumps with a stock suspended XR200. The intake, as well as the exhaust, are rather choked up on almost every Honda XR from the factory. You may not want to do every single modification depending on your riding conditions because some of the OEM parts are designed to protect the bike from possible failure.

The airbox helps keep the air filter clean from dirt and water, but there’s very few openings for air to get to the filter. By “opening it up”, it will allow more air to flow through the carburetor, resulting in a noticeable increase in throttle response and power. To do this, the best way is to remove the snorkel on top of the airbox. Just remove the top cap part and keep the other piece that has the three ducts/openings. More water can get in if you ride through mudholes, but it’s still protected because you’re just opening the airbox on the top.

Another intake mod is replacing the stock filter with a bigger and more free-flowing air filter. This will let that new air actually reach the carburetor and use it to make a little more power. If everything else is stock, you shouldn’t have to re-jet the carb because the XR200 comes rich from the factory.

Exhaust

This is another modification that may require some compromise. If you need your XR200 to stay quiet because of neighbors or rules/regulations, you probably won’t find anything quieter than the stock exhaust. You can pull the baffle out for a good improvement in throttle response and low-end torque. However, it will be considerably louder. The stock head pipe also restricts the bike, so replacing it with a larger diameter aftermarket pipe will yield noticeable horsepower gains throughout the RPM range. XRs Only sells a stainless pipe that is meant to go along with their silencer. I have not personally tested this head pipe with the stock muffler, so I do not know if it will bolt on due to the larger diameter (however, this is on my to-do list and I report back when I find out for sure).

You can look for a supertrapp exhaust, but the consensus is that this is quite a bit louder than stock as well. If you want to be stealth, then the complete stock muffler is the best choice. On the other hand, a number of XR200 owners have swapped out the baffle that is held in with the bottom two bolts for the stock baffle from an early to mid 80’s Honda ATC 250R. It is not much louder while giving you back the performance similar to running it without a baffle due to it flowing better.

Engine

If the engine starts and runs strong without smoking, it’s probably the last thing I’d look at as far as mods. Why? Because it’s the most expensive, and the other mods should be done first to “un-cork” it. If you really want to add some torque and horsepower, there’s still some room for improvement in the cylinder and head. A hotter camshaft alone will make a good increase in power. However, the more radical the cam, the more supporting mods you will need to make it worthwhile. These mods may include an aftermarket exhaust, a high compression piston, better valve springs, and may possibly require some more piston clearance if you go really big.

There’s over-sized pistons, but if you bore the cylinder too big, reliability will be compromised. A stroker crank is also an option if you can find a shop that still does it for the XR200 engines. The 218cc stroker will mainly increase low-end and mid-range torque, so it’s a great mod for trail riders and those who don’t rev it out much. Powroll supposedly still does work for this bike, but you will have to call and see what they have to offer.

An XR Is Just an XR

There’s so much that can be done to these bikes, but in the end, it’s still just a 200cc (give or take) air-cooled, 4-stroke engine from 1980. If you care more about traction than power, this is the engine to start out with. If it were me, I would start out with the suspension and get it set up for your weight and riding style. This goes for any year XR200. Some of you may have a head start with the late 80s forks and adjustable shock, but it still may be too soft. If you can’t ride through the woods without bottoming out all the time, more power will not make you faster.

Once you get the forks and shock dialed in with the correct rate springs, oil, and damping changes so that they’re balanced, then you should move on to the go-fast modifications. An un-corked intake and aftermarket exhaust will produce a high percentage increase in power, but possibly at the cost of noise. If it still needs some more “oomph”, throw a cam and HC piston kit at it. Anything past that is going to cost hundreds or even thousands more.

Why would I personally do these mods? Because I bought a 2002 XR200R to slowly build up for my single-track and billy-goat, mountain bike. This is my plan for a long-term bike build, and even with an almost stock bike, it’s still a blast to ride.

For those that are crazy about making a lightweight bike even lighter, stay tuned for a future article on how to build a sub-200 lb. XR200 on a budget!

-Tom Stark

How To Convert A Dirt Bike To A Street Legal Supermoto

Motocross Hideout includes anything dirt bike related, even if it is ridden on asphalt. So, just what is a Supermotard? Yep, a dirt bike with sport-bike style wheels and tires for riding on the street. If you’ve ever ridden a dirt bike on the street, you’ll know how exhilarating it can be when you whack the throttle and the front wheel comes off the ground. Motards are the ultimate hooligan bike, and can get you into a lot of trouble if you don’t follow the rules. However, if you want to legally ride on the street or go to track-days on a road course with your dirt bike, here’s some things you will need to replace or install.

Wheels

If you want to convert your dirt bike to a supermoto, you’re going to need ‘Sumo’ wheels and street tires. 17 inch wheels, front and rear, are the most common for supermoto, and are much better for street riding than the stock 21/19 that are stock on most full-size dirt bikes. They lower the bike, they handle better, and they’re wider so you can lay more rubber down. 3.5″ width is typical for front supermoto wheels, and 4-5″ are the most common for the rear, with several in between. You can go wider or narrower, but you may run into tire width issues, as well as the wheel being too wide and rubbing on the chain and/or swing-arm.

Tire size selection is important in order to make your motard ride right. If you have a rear tire that’s too wide, it can actually hinder the performance. For example, if you have a 4.25″ rear wheel with a 160/17″ tire, the wheel will be pinching the bead of the tire because it is wider, thus creating a more extreme profile with a smaller radius, and ultimately less road surface. However, if you put a 150/17″ tire on the same wheel, it will have more contact surface on the road and perform better than the wider tire. This is research that you should do for your specific year and model bike to determine what combination is best.

Supermoto Wheels
Supermoto Wheels

 

There is also the more extreme route for those that have the machining ability and want to possibly save a few bucks. Street bike wheels from certain bikes can be retrofitted to work with your dirt bike. However, there is usually machining involved to make clearance to fit on the swing-arm and/or forks. Bearings are fairly easy to swap out, but you’ll either have to find wheels with the same size bearings as your dirt bike to fit the axle, otherwise you have to buy some bearings with the correct size inside and outside diameters. Another problem that may come up if you choose to do this conversion is mounting the caliper. This depends on what size rotor you’re going to use, or if you want to put the stock caliper on the wheels you’re using. I can’t recommend a certain set-up for everyone, as there are so many different bikes and combination of wheels. Unfortunately, that is where YOU will have to read-up on as well. I don’t recommend going this route unless you are mechanically inclined and have the machining capabilities/resources. Lastly, cast wheels are not as strong as spoked supermoto wheels, and they will not be able to withstand the abuse of jumping and off-road riding; just something to keep in mind as well.

Lights

Lights are required if you’re going to ride on the street. Every state is different, but the usual requirements are a headlight (hi/low beam), tail-light/brake-light, mirror, turn signals (hand signals are OK in some states), and reflectors. Headlights are fairly easy to install if you carefully read and follow the instructions (I know, that can be hard for the guys…). However, if you are using a motocross bike, you will either need an alternate or bigger power supply. An upgraded or rewound stator is probably the easiest way to go because that alone will power the lights. You’ll need to get a regulator to go with it so you don’t burn the lights out.

Lighting Kit
Lighting Kit

Unfortunately there’s not an aftermarket stator for every dirt bike, or at least one that’s reliable. Another easy way to get usable lights for your street legal conversion is with battery power. You can buy an aftermarket lighting system for most bikes, such as the DRC EZ electric wire kit. It is powered by a battery pack of 8 AA batteries that are easy to swap out. They will last several hours, depending on how many lights you have and what kind of wattage they pull.

Another option would be using rechargeable Lipo batteries, such as ones used in RC planes and cars. They should be 12 volt (4 cell) to match the lighting system. This route requires a little more initial cost, but being able to recharge the battery makes it easy, especially since you don’t have to worry about carrying around a bunch of small AA batteries.

Brakes

In order to go faster, you must be able to stop faster. If you’re converting your dirt bike to ride on the street or asphalt, you will want to upgrade the front brake. The rear brake isn’t as important because it’s not doing as much braking, so it’s adequate for most riders unless you’re highly competitive in supermoto racing. The brake-system is fairly simple in regards to modifications. You have the master cylinder, brake line, caliper, and rotor. The quickest way to get more braking power is by replacing the rotor with a bigger one because it produces more leverage. 320mm is a popular rotor size for motards to have, but there’s some things you’ll have to consider.

Most bikes can use the stock caliper with a larger rotor, but the stock location will not work. This is why you must buy a relocation bracket in addition to the rotor. Be sure you buy the correct bracket, though, as the size/brand of rotor and caliper may vary. Calipers with four or six pistons are a common upgrade, as this will also produce more stopping power.

A steel or aluminum braided brake line is a fairly inexpensive accessory to your braking system, and they perform better than the stock rubber hose. They are built to withstand more pressure, and give you a more consistent and less “mushy” feel compared to stock.

Upgrading the master cylinder can get expensive, but if you are racing and want the most power with less effort, a better Master will complete the package. There’s quite a few options out there to choose from, and generally, you get what you pay for. On the flip side, many riders on a budget find an MC from a different dirt bike, street bike, or even a quad that is better than what they already have. Remember to do some research as to what works with your specific bike if you decide to upgrade.

Sumo Front Brakes
Sumo Front Brakes

Accessories

Last, but not least, are the ‘accessories’ that you must add to your motard to make it “street legal” and pass inspection if needed. Every state is a little bit different, so I will just hit the basics on what’s required. Almost, if not every, state will require a working horn. This doesn’t have to be anything fancy. In fact, a lot of riders buy a cheap bike horn from wal-mart. Turn signals may or may not be required. Hand signals are legal in some states.

Most states need a headlight with a hi-low beam headlight, as well as a working tail/brake-light that works with the rear brake. Reflectors are a good idea, whether they’re required or not. It will make you a little easier to see, and if you get pulled over, the deputy may take you more seriously if you add little safety things like this. You will likely need a mirror to be legal, so a simple handlebar mounted or bar-end mirror will work.

A road-legal exhaust is a good idea if your bike is being inspected. Most dirt bikes have “For off-road use only” stamped on the stock exhaust, which isn’t going to fly if a cop scrutinizes your motard. Also, bikes that carry passengers must have an appropriate seat set-up and passenger pegs. I know that supermoto’s are solo-bikes 99.9% of the time, but it’s just something else to keep in mind.

Now it’s time to start building your bike! All of these parts add up quickly, which is why properly set-up supermotards (especially when plated) are so expensive to buy used. You probably won’t get your money back when you go to sell it, but it can be worth the money to know that you built it with all of the parts that you want. If you do some shopping around and have the whole winter to piece your bike together, you can find some good deals on used or even new parts. Besides, if you buy a complete supermoto kit for your dirt bike, you can always go back to the stock set-up if you want to ride in the dirt again.

I know that was a lot to take in, so you should bookmark this page/website and come back to it throughout your build. If you just want to see all the parts involved in making a supermoto, here’s a simple list (how far you want to go down it is your decision):

  • Supermoto wheels and street tires
  • Street gearing/sprockets (depends on what kind of riding you’re doing)
  • Headlight
  • Tail/brake-light
  • Upgraded stator or battery system for lights
  • Larger front brake rotor and relocation bracket
  • Better front brake caliper and master cylinder
  • Turn signals
  • Mirror
  • Horn
  • Hi/low beam headlight switch
  • Reflectors
  • Street legal exhaust
  • Passenger seat/pegs

If you have any questions, either post a comment below or click the Contact tab above and shoot me an email. Have fun building your own Supermotard, and ride safe!

-Tom Stark

CR250/CR125 PWK Air Striker Conversion – Throw Out The TMX

Tired of having to re-jet your Mikuni TMX carb after fouling plugs over and over again? It’s no secret that Honda’s Mikuni carbs on their CR two-strokes in the 2000 era are poorly jetted from the factory. Not only are they jetted pig rich, but they are finicky when there’s a temperature or altitude change. In the morning you may have a 45 pilot and the needle at the third clip, but in the afternoon you may have to put in a 40 pilot jet with the clip in the second position, otherwise it will cough and blubber.

The new popular mod for 2000 and newer CR125’s and 2001+ CR250’s is swapping out the TMX carburetor for a Keihin PWK Air Striker carb from another bike. These carbs are relatively easy to find, as many other bikes had them. The good news is that they are cheaper than most bolt-on aftermarket parts. Even a brand new one can cost you under 200 bucks. For the difference it will make, many late model CR owners says it’s night and day better. The bad news is that not all of them are the same as far as fitment goes. Read on to find out which will fit your dirt bike.

What Makes The PWK A/S Carb Better?

To simply put it, the PWK Air Striker is just a better overall carburetor compared to the stock TMX, or even the older Keihin PJ. It has the same bore as the previous models, but it’s not the same carb. The Air Striker has quad vents, as well as two fins on the inlet side. There are some other minor differences, but those two are the major ones. It’s designed to prevent bogging when the bike goes over whoops or jumps. The throttle-response is crisp from idle to redline when jetted correctly. CR owners that converted to the A/S rave about how much cleaner it runs from idle to half throttle.

Some say that you can get the Mikuni to run just as well, but it’s not going to be as consistent. Most people that do the swap say that it’s a set it and forgot it modification. So unless you’re going from sea-level to the rocky mountains, you’re not going to be chasing your tail with jetting changes throughout the riding season.

There’s More Than One Style PWK?

I have spent many hours researching this PWK carb conversion, so I decided to write this article to save YOU the time and money of doing it yourself. Since most people are only converting their CR250’s and CR125’s (some put it on the CR500 as well), it’s a little bit easier to determine which ones will fit. This guide will save you the time and headaches you could be having while trying to re-jet your Mikuni TMX Carburetor…

Before I confuse you with all of the different Keihin PWK carburetor models, I’m going to show you how to tell the difference between them. Scroll down to see the picture, and I will go from left to right, describing the differences in length and electronics they have.

  1. The first one on the left has the black screw top, and is the older style “long-body” PWK Air Striker. The body length is the distance from the tip of the inlet to the tip of the outlet, and on this one is 91mm. There are no electronics/TPS on this one.
  2. The second PWK is the newer style short-body Air Striker. It has two allen screws on top, and has a TPS (Throttle-Position-Sensor). The short body length is 75mm from inlet to outlet.
  3. The third one is the same as the second, except it does not have the actual TPS; just the spot where where it would be. The allen head screws on top also mean it is the short-body style.
  4. The fourth one on the far right is the standard Keihin PWK carb and NOT the Air Striker. The Air Striker is identified by the two “fins” on the inlet side, roughly at the 5 and 7 o’clock position. While it is still a step above the Mikuni TMX, it’s not as good as the PWK Air Striker.

Also, all of these PWK carburetors have the same size inlet and outlet diameters. Although their lengths may vary, they will all fit over the same size intake boots. The older and long-body style has the screw-on cap, and the newer and short-body style has the 2 allen screws cover.

All Versions of the Keihin PWK Carbs
All Versions of the Keihin PWK Carbs. Photo Credit: hallsy on ThumperTalk

First:

  • Screw cap (black)
  • Long body (91mm)
  • No electronics/TPS
  • Air Striker Quad-vent

Second:

  • Allen head cap (2 screws)
  • TPS (Throttle-Position-Sensor)
  • Short-body (75mm)
  • Air Striker Quad-vent

Third:

  • Allen head cap (2 screws)
  • No TPS, but has the spot for one
  • Short-body (75mm)
  • Air Striker Quad-vent

Fourth:

  • Allen head cap (2 screws)
  • Standard, NON-Air Striker Carb (No “fins”)
  • No TPS
  • Short-body (75mm)

Now to find out which PWK A/S will fit your motocross bike, you must determine the year of your Honda CR250 or CR125. The 2000-2003 CR125’s have the older, long-body style with no TPS (85mm length). They will need the longer A/S with the screw cap, which is the first one on the left in the image above. The 2001-2003 CR250 also uses the same carburetor (the ’00 already has the PWK A/S). The 2004 and newer Honda CR two-strokes have the newer, short-body (75mm). If you can’t remember that, just remember that if your bike doesn’t have a TPS carb, then you need the older long-body with the screw cap. If it has a TPS, then you want the newer short-body with the two allen screws and TPS PWK carb. However, there are people that have put the long-body on the ’04-’07 CR250 had it worked fine. You just won’t be using the TPS.

There are some people using TPS Air Strikers on their bike that originally did not have it with no problems. They simply do not use it, and it does not seem to affect it. If you just need one cheap and that’s the only thing you can find, you can make it work as long as the length is close to what the stock carburetor is.

What Bike Can I Find One On?

Unfortunately, I cannot go through every single year of each model that had a PWK air striker and which bike it will fit. I’ll just give you a quick run through of the bikes that could have it, and then you will have to determine if it will fit yours. Don’t worry, just follow the guidelines above and you will be fine. Remember that just because the seller says it’s a PWK Air Striker carb does not mean it is. The easiest way to tell is if it has the two fins on the inlet side. So, onto the list of dirt bikes that have it (some years had variations of it, so pay close attention before buying it):

  • ’01 and newer Yamaha YZ250 w/TPS
  • ’98 and newer Kawasaki KX250 w/TPS
  • ’98 and newer Suzuki RM250 w/TPS
  • ’99-’00 Honda CR250 long-body w/out TPS
  • ’02 and newer KTM 2-strokes (some are the Air Striker, while some are the standard PWK, as well as 36mm)

Starting Point For Jetting

CR250:

  • Elevation: 1000ft
  • Main: 175
  • Pilot: 45
  • Slide: #7.0
  • Needle: Third clip position (Cxx/R13xx)
  • Air Screw: 1.5 turns out

CR125:

  • Elevation: 1000ft
  • Main: 180
  • Pilot: 50
  • Slide: #5.5
  • Needle: Third clip position (Dxx/R14xx)
  • Air screw: 1.5 turns out

The 1999 CR250 A/S is the easiest starting point for the CR125 because it has the #5.5 slide. It is richer, and 125’s require richer jetting than a 250 with the same carburetor. The best starting point for CR250’s are with the ’00 PWK A/S, as it has the leaner #7.0 slide.

Do I think a Mikuni can be jetted to run as good as the PWK? Probably, but with a small temperature or elevation change, you’ll be needing to swap jets or messing with the needle again.

I tried to cover everything you need to know and make it as easy to follow as possible. If you feel there is some information that is missing or should be added, feel free to comment or send me an email.

-Tom Stark