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

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19 Comments

  • Chris says:

    Thank you very much. Best article i have read on the conversion, very helpful!

  • Joseph says:

    reading the form about changing out the carb on the cr125 bike, can you tell me if this is the correct part number that I would need for my 2003′ cr125r
    KEIHIN 38MM PWK38AS AIR STRIKER CARBURETOR, CARB KXT TECATE LT250R

  • Tom Stark says:

    No problem, glad you found it useful!

  • Tom Stark says:

    Yes, that carb will work on your CR125. You will probably need to re-jet it with different size jets, needle, and possibly a slide.

  • Joseph says:

    Thanks for getting back to me, could you do you know what size jets, needle and slide I may need? Any info would be very helpful I’m not much of a mech when it comes to carbs on a dirt bike, I was hoping that I could slap on the new carb and do some simple adjustments.

    Thanks again

  • Tom Stark says:

    A good starting point for the CR125 is posted above in the post. However, every bike is a little different. It really depends on where you live (climate/elevation), as well as what modifications have been done to the bike. Those jetting specs are just recommended, but you may not have to adjust to all of them. If you live within 1500 ft. of sea level I would suggest starting out with those size pilot and main jets, though, and see how/if it runs from there.

  • Joseph says:

    Once again thanks for the quick response, I live in Phoenix, Az as far as mods I have FMF pipe & FMF Turbinecore 2 Spark Arrestor & Moto Tassinari Delta 3 Reed Valve System. I thought that size needle,main jets, polit came with the new carburetor. Anyway thanks again.

  • Tom Stark says:

    No problem. If you’re getting a new carb then you may be able to choose what jetting comes with it. Good luck!

  • Giuliano says:

    Hi, I´m speaking from BRAZIL, I´ve read this article several times so that I decided to do the PWK conversion on my 07 CR 250 (just waiting the carb arrive here).I´ve chosen one form e-Bay pre-setted for the bike wich comes with an appropriate throtle cable too.
    About the TPS cable remains one doubt, may I simply disconect it after bolting the Keihin PWK? Is it possible to keep it puggled?
    What would be the best solution?
    Thanks in advance!

  • […] of messing with the dumb bar-mount choke on the TTR, you can throw that out as well with this new carb conversion. The choke is mounted right on the new carb itself. In fact, a lot of owners of this swap say that […]

  • […] a great bike. You just have to fix the carburetor right way. Unless of course you go with the PWK Air Striker like many people are […]

  • SCOTT says:

    Which size carb do I need to run it looks like keihin offers a few different sizes. I have an 02 cr250. would I run the 38mm one?

  • SCOTT says:

    also do I need a new throttle cable??

  • Tom Stark says:

    A 38mm will work best in most situations if the bike is relatively stock. Get the older screw cap style if you are converting to the air striker. And no, you shouldn’t need a new throttle cable as long as the old one is still good. Bolt on and go!

  • jason says:

    Hello, I Bought a new a/s body and built it with the recommended settings from the page above. Its for an 02 cr 250. The bike blubbers in the mid range and barely makes it into the high rev area of the powerband. I used a one size leaner needle on the ssecond clip and it seems bettrr but its not right yet. My plug is dry and very dark brown but there is a small amount of spooge on the end of the shorty. Its a stock bore, vforce 3, fmf fatty with shorty. I cant imagine going leaner on the main jet but what do you think? Ive been out of the sport for 5 years and just picked the bike recently. Im at 800′ and typically high humidity “Michigan”. If the rc cables are stretched could this cause the blubbering? If the servo is bad could that cause it? I had a heavily modded 01 before and the 02 seems weak compared to it. I wanted tge final generation frame….. trade off. Any help is appricciated

  • Tom Stark says:

    Have you checked the engine compression recently? The recommended jetting is more of a starting point, so you may have to adjust a little bit. A dark plug would indicate that it’s running rich. With that said, the pump gas these days isn’t very good, so that doesn’t always give an accurate reading. I would go leaner on the needle and main at least one. If it gets better then you know you’re headed in the right direction. Also, which of the PWK’s did you buy?

  • Braaaper121 says:

    Awesome article. I ordered a air striker for my 07 cr125. I know where to buy jets and needles but where can I buy a slide at?

  • Tom Stark says:

    That is a good question Unfortunately, they are hard to come by as not many people sell them as an individual part unless you buy new. You’ll either have to do buy multiple PWK carburetors that have different slides, like I did, or wait until one pops up on eBay or forum classifieds such as Thumpertalk.

  • Fabio says:

    Hello from Sardinia. What about the second one from left with power jet? What should we do with it? Thank you very much

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