125-200cc Walt's WR-144 Mikuni TMXX Jetting Revealed!

Nice work on the carb!

Yeah, Ron does nice work. Looks like his low speed mod involves removing the starting jet and replacing it with an orifice. Probably more than that but that's what I can see. I'm going to start out with a 30 pilot and a 470 main. Should be close.

Got to finally ride the bike today with the RB Designs carb mod and I can say it is more than worth the money! I thought that Walt's jetting was the best setup you could have for the Mikuni TMXX because it ran so clean but this bike now rips very hard right off the bottom. No trace of a bog anywhere. This was pretty close to sea level and tomorrow I'll be riding about 4000 feet. I haven't changed the powervalve springs yet but I'm planning on doing that tonight. With the stock spring, the front end is in the air every time the powervalve opens. Also discovered that I need a steering damper after a high speed run that ended with a pretty good tank slapper!

5.0 slide (4.0 modified by RB)
470 main
30 Pilot
6CHY16-61 needle (middle slot)
AS: 1-3/4 tuns out

For tomorrow, I installed the orange large and green small springs in the governor for a range of 5000 to 7200 RPM for the opening. I don't know how the bike could get any better but thanks to Walt we have options!

Awesome! Ron's carb and head mods on my son's 2011 TM MX250 made huge improvements also.

Doug,

I haven't had much luck with that combination. I would try the stock and silver first. Then if that works but you want to get the PV's opening sooner then try the white and silver. Work down from there until you start to get a bog when the PV's open. The biggest problem is the pipe timing is for the 7K to 12K rpms. You start opening the pv's completely too much before that and the bike is going to gasp. I ran the orange and silver for a while and it was not the best. Kevin's 04 CR125 ran great with the yellow and green and even better as a 165. These tiddler Huskies tend to vary from one to the next as you know.

I also tried many of Walt's spring combinations and ended up with stock/silver. I never thought about it but the above explanation of the pipe timing makes perfect sense as to why the spring combos that let the PV open earlier didn't work for me with the stock pipe. I have an FMF pipe on it now so I'll need to try a softer outer spring and see what happens.

Glad to hear it's working out good for you and sounds like a good fix with new WR ignition. Sounds like you got a winner.

OK Walt. I swapped out the large orange spring for the large white spring. First time I did the swap it was over an hour. This time about 15 minutes. I think it will pull it fine with the RB carb mods and the 2002 Procircuit pipe.

Sounds good Doug. I really look forward to hearing how it works with that combination.

Well it ran awesome. No problem at all. The powervalve came in with no bog and transitioned smoothly into a ripping top end! I'm thinking this RB Designs carb mod will make it possible to run any spring combination that you like. Next time at this altitude I will drop to a 25 pilot though. It was just a little blubbery just off of idle. This bike is running so well that I can let it slow down to almost idle speed in any gear and whip the throttle open and it just takes off.

Awsome news! I really liked the look of the procircuit pipe and think it has a broadening affect with a little more head pipe and longer tapering final cone. One of the better 125 pipes that I have seen for this bike. That and the RB carb definitely made a difference for you. Cool stuff.

Thanks so much for developing your powervalve spring kit!

Should be able just to raise clip a 1/2 clip or 1 full clip. So you don't have to mess underneath.

If you have to move your clip, use one of those cheap, zip loc bags. Just cut corner out for your needle nose pliers to be inserted. You'll never loose your clip while on the trail or at camp or home.

Dont use pliers, bad juju. Lay the needle on a flat surface (fenders work, or a rock, workbench is even better), lay it so the opening of the clip is down, grasp needle with thumb and index finger just below the clip, put index finger of opposite hand above the clip, press down, the clip will still be in the groove but released from the needle, it will not fly off. i re-apply the same way. Never lost one yet. The needle never really touch's the surface durring this process so bending the needle isnt an issue.

Hey Folks,
Got a chance to ride my 2012 WR with the RB modded carb. Only got to put 15 miles or so before a crash took my nephew's clutch lever off (and banged him up a bit) so we had to head back and consume some liquid beverages! Rode mostly single track and some very fast (and fun) south jersey fire cuts. Had the plate, bore, low speed mod, slide cut to #5 and the thumb screw. Put in the RM needle and also purchased Walt's PV spring kit. I used some suggested settings (thanks Darty!) and it is a totally different bike that is good off bottom and has a very hard mid range pull. I agree with everyone here that has had the carb done by RB.....if you do nothing else get this mod done and buy the RM needle.

I do feel that it seems to shuts off early on top. This may be due to a combination of not riding/racing a 125 since 1999 and being used to a 2007 TE450 that never seems to stop pulling on top. It runs clean and crisp through the whole throttle range. I'm thinking of going up one on the main to see if it changes anything up top. I'm not saying I "need" more top, just feel it should have a little more. I could be wrong though.

I have the stock PV spring with the silver inner spring installed but I may try to get the PV to open slightly sooner to see how I like that. I have to admit, I LOVE the hard hit of the PV's when riding a 2 stroke and it keeps me riding "aggressively" I'm not so sure I like a "smooth" transition so I will be fiddling with Walt's springs. I have adjusted the PV arm to about 3/4 of the way up.

I have a 52 tooth rear that I'm going to throw on for this weekend and that was one of the first mods I did when racing enduro's with my 125's. Don't get me wrong, this bike flat out rips, handles like a dream and is an absolute blast to ride! Just have to get that "personalized" feel to it.

It's great to be able to come to a site like this where everyone is out for a common goal.......having fun doing an awesome sport with a bike performing at it's full potential Thanks again to everyone.

Settings:
RB modded carb
35 pilot
470 main
6CHY 16-62 needle middle clip
mix screw 1 1/2 turns
#5 slide (RB cut of my original #4)
stock gearing
stock PV spring with silver inner

Try couple of things:

Did you drill those holes lil bigger in your bowl and bottom carb nut?

Mess with float level to make sure enough gas is getting to your main?

Also, if you try going up on main, try going 460 main. You could be lil rich on top of the divider, which can. Hold your top end back little.

Yep, drilled the holes. BTW, do you make the little holes in the plastic splash cover around the jets larger too?
Checked float level and is right around 8mm. So you think I should "drop" one on the main first? I did pull the plug and it looks a "tad" rich but the last 3 miles or so was ridden at low/mid throttle only so not really an accurate read on the main.

No don't drill plastic cover. Try 7mm float height.

Evans 125 and my old 125 lost lil topend with 470 main. Ran the best around 460 but still try your 480.

Just thought, go have sum fun!