125-200cc 09 Wr 125 Bog/Performance Solved?

Well, I tested all day Saturday and the bike is still not perfectly jetted. I have it close. I settled on using the Keihin PWK this weekend. It seemed more consistant and good low end and decent top end. Maybe not quite as strong on top as the Mikuni but close. I still have a bit of hesitation / blubber at the transition point. Not as bad as it was. I checked the plug after the race and it was sooty black so I think I can lean it out a bit more. I tested the Mikuni several different ways. If I got the blubber out of the midrange transition point then I go the BOG back. It likes to be rich in that area but I couldn 't find a happy point. I shimmed up and down changed clips and needles. I still ended up with the 40 pilot after testing a 42.5. Still seems like it needs a bit leaner. Finally I gave up and late Saturday I swapped over to the Keihin PWK. I found it a tad rich in the middle so I switched over from the JD Jetting blue needle #4 position to the red needle #4 position. Better but still not perfect. So I dropped to the #3 positon and it was better still. I didn't have a leaner pilot but ended up with the airscrew 2 turns out. I know that the pilot is still a bit rich because when I started it up Sunday morning (About 35 degrees) , It started first kit and I immediatly too off the choke and it ran clean and fell to an normal idle and it was't even warmed up yet. I need one step down on pilot jet. About a 42 should be very close. Well after the Hare Scrambles (which I won my class by 5 minutes) , I pulled my plug and it was sooty black , Not wet but still mostly black. I still have some spooge coming out of my pipe. Not as bad as it was but still bad. I am now getting 16 mpg, Which is up from 15 mpg with the Mikuni. I think I can improve it still more.
I LOVE THIS BIKE

Congrats on the ride Keep working with the jetting and you will find your happy spot. I think Kelly was running the red in 3 or 4 with a 42 pilot. Keep up the good work.

Yes these new WR 125/144 are about as much fun as you can have on a dirt bike.

Congrats, you'll find what fits, just a matter of time.

Wally and Darty , I appreciate all the help and support you have given me thoughout this process. Without your help with parts and advice I couldn't have gotten through the process nearly as fast. (Darty, I am thinking of going to the #2 position Red needle and using the shim you sent to raise it to #2.5 position. ) Wally, What is normal timing advance in mm btdc and what do you recommend as a bit advanced timing BTDC ? This too may help that "SOFT" spot in the transition zone.

Vinduro,

Great, glad to be of help, anytime! Your the one doing all the painful leg work. By the way, I think your win was from a free enduro headlight!

OH, I want everyone to know that I am not using normal pump gas. I a blend of 3 gallons of BP Premium 93oct NON Ethanol, and 2 gallons 100LL AVGas. Do not run 100% AVGas as it is blended for low octane, low constant rpm at higher altitudes. BUT it is consistant and stable over a long time with NO Ethanol. The Pump gas gives it back characteristics of a gas meant for varying RPM in a high performance High Compression engine. The reason I mention this is that when using a race gas or a blend like I do , OR a 93 octane straight gas , allows for a leaner mixture over an oxygenated fuel like Gasohol. Ethanol will make your engine run leaner .
Dwight

OH, I picked up some extra jets today. I currently have a 45 pilot and 185 main jet in the 38mm PWK. I picked up a 40 and 42 pilot and 180, 178 and a 175 main to test with.

The elephant in the room. Many have posted that the Mikuni once jetted runs great on top and some posted better on top. Correct me if I'm wrong but isn't that what you want a 125 to do? All these posts looking for the perfect low end on a 125 at least until the weather changes. Maybe I'm being the devils advocate here but why not jet it to run up high like a 125 and ride it like a 125.

lankydoug - You can rarely have the bike at full throttle and need power down low - I dont care what level of rider you are . Keihin does give it more meat in the mid range also.
My older style Mukuni can let you down when you dont want to be let down - on a snotty hill
Keihin helps to tractor up the hills
I run the 170 or 175 main with 45 pj red needle in the middle or dropped one
raising needle one if it lean bogs due to cooler weather

If it is impossible to get usable mid-range out of the Mikuni I don't blame you for switching. I'm waiting for the arrival of my wr250 (should be two more days) and I'm reading similar posts about the carb on it. I had a YZ 125 in the old days that had a powerband like a toggle switch which is why I went to a 250 and a 200 when I decided to get back to the dirt. I guess I have trouble believing that there isn't someone out there stubborn enough to make the Mikuni work.

I too was shocked that I couldn't get the Mikuni to work. I have long been a Mikuni fan but I HATE the TMX. I wonder if I could stuff a Mikuni VM 38mm in there. A well jetting Mikuni VM rarely needed rejetting and always ran well. Lots of needles and needle jets to help with also. Maybe it doesn't quite produce as much power on top as the TMX or even the PWK but the VM always made such good low and midrange power you just didn't worry about top so much.

I think you can think you get it solved and then you have a problem sometime on the ride ... I ended up selling my old wr125 because of jetting issues but come back to the wr 125 again and have stuck it out and played more and also now use the PWK after some resistance.
Is the VM the old Husky carbs . I now they had 38mm Mikunis on Wr 125 way back in 83. They dropped to a 36mm then went back up to 38mm. I was thinking of trying a 36mm Mikuni from the YZ 125 - late 90s.
I think you have the TMXX Vinduro .. I still like the TMX for the smoothness of it and top end . But the little 125 and I need all the help we can get down low .

Vinduro - I saw you are using an avgas mix. I ran it in my old WR125 and when ran straight I had to go about 2 steps leaner everywhere and when ran half and half I went 1 step leaner. So you may have to adjust a bit from what others use for jetting.

That's kinda a mystery, because my TMXX is pulling down low more and all thru the top, than I ever got from the PWK. I spent about a month on the PWK and figured it needed a richer slide (like a 5, 5.5, 6) for roll on whack bottom and a thinner more tapered needle for transition up thru top end. I just took my son's TMXX off his RM so I can keep it for his 06 WR125 , as we sell the his RM. I put the PWK 38 on it, red needle was best, and lost top end on it even after pushing bigger mains to the limit, moving clips around. The mid range was awesome on it. It wouldn't run very good with the blue needle. Then I put the old TMX 38 on it and finally settled on a 40 pilot and 370 main. It actually, runs pretty good but still not like the TMXX. It'll be spring before I get the Eric Gorr 144 or 167 route repaired and on to try. Plus I am grinding away on the ports. I am still keeping the PWK to try on the bigger bores.

bingo. goes back to what i've been saying. 125's are top end motors. verify your main jet circuit first. my Mik runs fine. first kick in gear most times. carburetes cleanly. all it did was idle when i got it. would not go, at all. borrowed a baseline from kelly and the OM, little more fiddling and 20 mins later: meeeeeeeeeeeep!

want more bottom/mid? = more cubes, smaller carb venturi, more intial timing advance (dont do it). or all three. or just by a 500.

or just keep it WFO and sliiiiiiiiiiiiiiip the clutch like yer posed to. all the bottom end ya need right there. and, more traction as the flywheel is spooled up!

p/s- run pump gas. it's fine. mixing fuels and jetting to that is a sketchy recipe ! esp if one of those fuel sources dries up and you are leaned out for a recipe with same- squeak!!! oooops.
Av gas is for airplanes. Pump gas is for dirt bikes. Av gas sucks!!!
run pump gas at 40:1 for trail, 32:1 for long, fast WFO MX track racing/practice.

I am not advocating use of straight AvGas by any means. I am using a blend. Your Pump gas in California is worse than that in many areas. Most pump gas contains Ethanol which is terrible. Makes your bike run lean. Inconsistant mixtures. You don't know if you are getting 5% ethanol or 15% ethanol. Oil doesn't like mixing with Ethanol unless you are using Castor. The gas starts going bad in as little as 2-3 weeks and can clog up your carb in 5 or 6 weeks. Ethanol attacks rubber components in your carb and engine. Modern materials are better than those in older bikes but it is still bad. Ethanol draws moisture to it which can make your bike run even leaner. If you can't get non ethanol gas I recommend running non oxygenated race gas or blending 2 gallons of non oxygenated race gas with 3 AvGas. Do not run straight AvGas. If in a bind and you can't get race gas or non ethanol pump gas then, personally I would run straight AvGas over Gasohol. It will run a bit flatter but at least it won't harm your engine. AvGas should never be used as a substitute for race gas if your engine needs race gas. If you can get straight Pump Gas without ethanol in a 92+ octane then you are fine.
Dwight
Ag Pilot, Commercial Pilot , WWI Aeroplane enthusist.

i never said you were (straight av gas). re-read what i wrote and have written.

i've been using pump gas for decades 50:1 and aint had a problem yet. i know all about what's in our fuel. i also mix some up it use it then dump the rest in my truck if it sits more than a week- as iv'e advocated over and over. regardless of where it came from. and, again, Av gas is for airplanes, not dirtbikes.

mixing fuels makes it even more difficult to eliminate variables. run one or the other to eliminate variables. simpler is better and more repeatable, is my point.

pvduke- yer basic motorhead, tuner, wrench turner to the stars and all around nice guy.

I agree the gasahol is crap. Thankfully we have access to ethanol free premium gas here.

yeh, it's crap, none worse than where i am.

it's yet to cause and issue though. ever.

i just jet my bikes, 2 and 4T, to the pump gas that's most available and they dont ping or eat parts. they wont benefit from a custom blend of other fluids, and, it'll really toss things out of whack when one of them ingredients aint avail. these newer bikes are simply made to run on this stuff. not race gas or any varyation of same. i pull my plated '07 TC right up to the pump then roost off into the mntns w/o so much as a thought.