125-200cc Keihin vs. Mikuni for 150

I was running a 38mm PWK on my 09 150. I hated the fit and heard the RM needle made the Mikuni better so I gave it a try. It seemed good last ride and I decided to stick with it. But I hate to leave any performance on the table so now I am starting to second guess myself. When I tried the Mikuni it was only my second ride with a CR ignition and the first with a new fuel. So to really do a good comparison I need to try it back to back with the PWK and also jet the Keihin for the fuel I am using. This could waste a full afternoon so I am wondering if anyone has already done this test and could tell me the results. I thought the Mikuni was maybe just a tiny bit weaker on the bottom and reved out a little harder. But like I said I would really need a back to back test to be sure. I’ve read plenty here about peoples experiences with both carburetors but getting a review form anyone who has had both dialed in is hard.

Basically, who has used both the stock Mikuni and a Keihin, jetted properly, on a 125 or 150? Is there much difference?

If the Keihin is better I think I will get one from a KTM so it solves the fit issue. If the Keihin is not much different I will just use the stock carb and probably be taking it over to RB Designs for a divider plate (if he works on these carbs).

My 38 PWK is an Air Striker. That is different than a quad vent. Mine fits perfectly. Just like the Mikuni. I just couldn't get the TMX to work properly from day to day. I am really liking my 36mm but I did have to change the slide to a 6.0. The 7 will only work if you have too large a pilot jet in the bike.

I think all Air Strikers are quad vents. The ends are the same diameter it is just that the Keihin is about half an inch too long.

Do you know exactly which KTMs have the Keihin that fits? Also what sizes they are? I think they are all 36mm ones except for the 125/150SX but I am not sure.

My experience was, my '09 WR125 ran very well with the Mikuni and the factory supplied carb kit. Drew Smith rode my bike and thought it was good. He thought I didn't need to even play with PV springs. Kelly had a good deal on the PWK's, so I couldn't resist trying one, as everyone said they were the nuts. I chased the jetting all around on the Keihin. I put it on in the Spring last year and with variable temps, I just couldn't find a setting. It was worse than the Mikuni in my book. JD red needle improved things, but not happy. I put the Factory 144 kit on and the Keihin came into its own. I got an RM needle and thought about putting the Mikuni back on, but the PWK 38 works well on the 144/150, like it never did on the 125. I did get the KTM 150XC needle to try, when I start riding. I've been in snowmobile mode all Winter, but that's done.

The 36 comes on for sure 250-300, and pretty sure the 150-200 woods bike. I have not tried the rm needle in the mikuni, so I can't really give a fair opinion. The 36 does fit nice.
GP

I was riding around today on my 2010 CR 125 and noticed a bog down low. I wasn't riding too hard, but it was very noticeable. I've switched over to a 38mm PWK with a power now rear insert and JD blue needle with 45 pilot and 180 main jet. I'm going racing on Saturday and will give a report when I get back.

Once I installed the Keihin, just from riding down the lane I could tell that the bog was gone. It sounds much more crisp than the mikuni.

Contact me if you are interested in a 36mm KTM 150XC carb. It has the correct main and needle. BUT, it needs a 6.0 slide and 35 pilot. I can tell you whom to contact for over $100 off retail. I used the cable elbow from the Mikuni and the stock throttle cable. All PWK Air Strikers are Quad Vents but all quad vents are not Air Strikers. Both my 38mm and 36mm fit fine and are no harder to install than the stock Mikuni TMX. The JD needles are not nearly rich enough. I had to use a 2004 KTM 250SX NOZF needle in the 38mm PWK A/S in the #2 position (which is richer than the NOZI in the 36mm) 38 or 40 pilot and a 175 main. Probably could have used a richer slide like the 36mm. With a richer slide you can drop the Pilot one or two sizes.

BTW, where is all the KTM parting-out going on these days? There used to be tons of parts on ktmtalk but the new classified format seems to have put a huge damper on the volume of parts.

The JD needles seemed a little lean for me also after I cut the head.

As far as what years fit, I got a 36 off a 2008 200 exc, fit perfect .Same length as Mikuni. I feel I lost some on top to the Mik. ,but low and slow like I ride anymore works great .(I have a stock WR125) Have yet to try the RM needle/Mikuni combo, who knows could be the ticket ?

Mark,

Your impressions are spot on. The Mikuni struggles a little on the bottom but has a little more top end with the carbs being equal in the middle. Any of the late model ktm 125/144/150, 250/300 have the correct size PWK to replace the TMXX. You can find them in either 36 or 38mm. If you go with the 38 get the NOZF needle, for the 36 the NOZI is the better needle as Dwight pointed out. The JD needles are just too lean for this application. I swap back and forth between the TMXX and the PWK depending on where I am going. I currently have the PWK mounted up for my local extreme elevation changes if the snow will ever melt. As Norman pointed out the 144 is a lot easier to jet than the 125. You should have some power valves by Friday so that will throw another variable into the fire. It will pull a lot better on the bottom/mid so it will cover up some of the deficiencies of the tmxx. Bottom line with the RM needles you can approach the rideability of the pwk.

Thanks Wally.

Yes the JD needles were too lean, at least after I cut the head. I switched to av gas though (since our pump has alcohol and race gas is too expensive) and it likes to be leaned out one or two steps so it might work fine now, I have not tried the PWK with it though.

What KTM would have a 38? I assumed they were all 36mm except for the 125/150sx which I thought was a 39. I could be way off here though as I have not been following recent KTMs.

If the Mikuni is close (which it seemed to be from my test) maybe I should just stick with it. I am not sure if anyone has had the RB treatment done to one but I bet it would fill in the bottom some. I know the power valves will also give it some boost, I could tell the difference right away when I went back to my stock ones.

Your silencer went out today.

Mark,

I just spent a full day testing carbs (Last weekend on 2 identical 09 125 engines, except for ignitions), Old TMX, Newer TMXX with RM needle-5.0 slide, Pwk 38 AS. This is what I have found in my situation and some of the bikes will vary/altitude changes and etc......

For a stock Wr125. The ignition system plays a big role in how this thing spools up. I could not get the PWK 38 AS to work on my stock WR125 and the newer Mikuni TMXX/RM Needle/5.0 slide was the the best its ever run.

When I installed the CR ignition, It works great. Then I decided to try the PWK 38 again with MattR's winter jetting. It works great and gave me more snap bottom and I have lost a not very noticeable top. Basically, under 50 temps, 185 main, 47 pilot, blue needle 4th down. I will move shortly to 180 main, 40-45 pilot, blue needle 4th down. I think this carb works great with the Cr ignition.

Then I messed with the other bike 06 WR125 with your old stock WR125 Cylinder, First I put the newer TMXX on it with RM needle/5.0 slide. It flat out rips! Then I used the exact setting in the PWK carb off my 09 WR125/with Cr ignition, and bolted it on. I had a stumble when you whacked the throttle and it bogged (flat spot) every once in a while lugging between 3-4-5th gear. I also had an old TMX flat slide from when we bought the 06. It was modified with the carb dividers, both front and rear. I fitted it with a 40 pilot,460 main and the GAY 59 needle. I was playing around and ripping on the bike. We have a ditch with a culvert and some dirt against it that I use for a jump. I hit it and when I landed, I was still on the gas and almost flipped the bike in 3rd gear. You really have to watch this bike in 1st - 3rd gear. It really caught me off guard with the torque. It has a mild stumble cracking the gas in a trials like mode, whacking the throttle. I think it's in the pilot or a simple needle move yet. Me, I think the carb dividers in the front and the rear is what makes this carb this torquey, nothing else. I even pulled the dividers out and it reminds me of the PWK Carb.

I moved the old TMX carb, with dividers, over to my 09 Wr125 and not a stumble, nothing, and it is a torque monster with great top end. However, I like the way the PWK 38 AS is working all around , with a nice tractor like pull, from top to bottom. I don't want to look at the sky all the time. I moved the old TMX back over to the 06 and will leave it on there or use the TMXX with the WR Ignition.

I will soon move into the 144 world and will be in the same boat as you! I will probably focus on the PWK 38AS and have been watching Dwight's work with the 36. My 144 cylinder will be a little different because it is ported, gasket/case matched/ exhaust port and pipe matched/Walt's powervalve grinding/head cut.

Nice right up.

KTM tech specs show that both 150XC and 150SX have 38's.

great thread i'm right behind you guys...

the TMX will be sent to RB soon for a divider plate, 144 kit w/Walts PVs hopefully bolted together this wknd. i also have an RM needle, various jets and 0.5 - 0.3 gaskets to try out.

I am really interested in how the newer TMXX works with the dividers.

What's the float height spec for the TMX?

Newer style is 6-7 mm and it needs to be accurate because the carb tilts forward a little.

Good! Mine's at 6. Thanks!

Ron at Rb is doing my TMXX right now and should have it back shortly, From what Tammy (Woodschick ) has said Eric is really happy with the divider plate in his TMXX. Iam putting together the pieces to do a 167 build and want to attempt to use the the TMXX.