Did he set it all back to stock and eliminate the stumble? I missed that.

Still, a chance to swap what is working for questionable parts is an easy verification.

• If the CDI swaps out and the donor either stumbles with the questionable unit or the problem bike runs with the doner CDI, problem solved. Get a new CDI box.
• If the carb swaps out and the donor either stumbles with the questionable unit or the problem bike runs with the doner carb, problem area located. If that's it screw it, go buy a flat slide!

Seen the swap technique used quite often when in an iffy situation and there is a comparable model in inventory (no customer bike stuff used) to swap out.

 

I hope PWJM doesn't mind if I divulge that the CDI swap with TheWack produced no difference in symptoms.. PWJM's CDI is apparently working just fine..

PWJM's bike will run without symptoms if set to very lean - I'm not talking my idea of lean - I'm talking DJ124 lean !!!!

Anyone who thinks that is not so bad, go ahead and pull your airbox lid and stick a DJ124 in your bike.. If Snowdrifter's bike responds the same way to an extraordinarily lean setup, then these two carbs are very different from the "norm" in how they are fueling..

So I think we are back to irregular carb fueling.. Still need to hear from Snowdrifter about his latest findings.. Coil RnR and Choke plunger check...

For me, next on the list is to, somehow, compare MAJ sizing..

We need to hear from IceBikeDave - who is, I think, out resident MAJ specialist..

 

Did they have a chance to switch carbs?

Could they measure their MAJ size using very small drill bits and seeing the largest that will fit?

 

This is a bit of a shot in the dark, since the configuration is different, although the symptoms are much the same. On my 2009 KLX250s, it came with an FMF PC4 exhaust, but hadn't done a jet kit yet (I hadn't had the carb apart, so I wasn't actually sure of what was in the carb yet). My 2011 had an FMF PC4, Dynojet jet kit and Snorkel removed. So, I removed the snorkel from the 2009 (so it was like my 2011, assuming the PO had jetted it, if he had the FMF on it). Took it for a ride, and had pretty much the exact same problems with the stumbling in that RPM range. I put the snorkel back on and problem solved. I eventually bought a dynojet jet and jetted the bike, then removed the snorkel, and it ran fine. Since the OP's carb is jetted, this doesn't seem applicable, but it does, to me, indicate a lean condition at those RPM's. I wonder if putting the snorkel back on (I think the OP had it removed?) would make any difference, and if so, that would mean larger main jet and/or different needle position?

 

First post he stated he ran it with & without the lid, no change. Which seems impossible to me. If I take the lid off, my bike runs like the problem he has.

 

He did lid on and off using different carb setups - you can't pull the lid off just any old carb setup without inviting horrible leanness, bogs, and other antisocial behavior..

 

Hey Guys, sorry for the late update.

First and foremost, big thanks to TheWack. He was a gracious and knowledgeable host. I got to see his custom / modified cam chain tensioner first hand and it was a pretty ingenious design for people who have the tools to pull it off!

Primarily I'd like to point out as KLXster says, we've ruled out any CDI or electrical issues so far.

Getting to the meat of the issue, we started out by riding each others bikes first (lol, who wouldn't?). TheWack was unable to reproduce my issue while he was riding and I'm sure he thought I was just making things up or something! I hopped on the bike and had to put the bike in 6'th gear and drag the brake really hard to get it to stutter at all, and even then it was pretty minimal.

The elevation change had made a giant difference. I live at 2000' ASL and TheWack is basically sea level. The bike felt pretty good, a tiny bit slow in the mid range, but top end felt good, I bet a 138 @ 2N would have been pretty good. I was able to pull a decent 2nd gear wheelie with the clutch for the first time ever.

We swapped carbs and as you'd suspect the issue was gone. Now TheWack rides a DJ124 with a lid on so my bike was running lean and the power was down a touch. As a way to doublecheck the carb we put my carb back on with the same jetting and the behavior of the bike was identical. Mid-range was much livelier, top end power was down... no bogging. After determining that the issue wasn't electrical and was indeed a fueling issue, we had stuff to do and parted ways.

So to recap, leaning the bike out fixed the issue - but I already knew that helped, I just hadn't gone THAT lean so far as to eliminate the stuttering entirely.

The bike is much more rid-able from 4k to 7500 now. I'm going to put a 128 in and see how it goes. At this point I could sell the bike and other riders would probably never be the wiser, but there's a problem and this doesn't sit well with me...

Other riders on this forum are using the same set up as me at over 5000' ASL with a 132 Jet. Nearly twice the elevation and they're using a bigger jet than me without any of these symptoms.

SOMETHING is causing the bike to massively over fuel the mid range. Properly fueling the mid range robs the top end of power and vice versa. I think KLXster is on the right track with the MAJ, because frankly, I don't think it could be anything else at this point. Nothing really explains the inconsistency of the issue while i was jetting at 132 - 138. At 138, after doing a re&re on the original coil, the issue was the least severe it had been since I added the slip on.

To reiterate my original post. I've tried a variety of jet settings and airbox set ups to little effect. Going so far as to run a DJ132 with the needle at 2N. While the issue was nearly gone at this setting, the bike had pretty poor performance in general (muted mid and top end).

 

pwjm, I am now running a DJ132 main, 3N for 2 weeks at 5k feet and the bike runs great. I'm also convinced as you are that there is something wrong. I'm glad now you at least know it's fueling/carb issue.

If your bike runs good with a DJ138 main, that would mean to me that your top en carb fueling is working well, according to klxster's dyno runs. DJ124 even at 5K feet has no power at all so that to me is normal that you have no power with it.

I would leave in the DJ138 and troubleshoot the mid range fueling. There must be something wrong and not just incorrect jetting. If I can run 132/3N at 5K feet with no issues, you should be able to run 138/3N at 2K feet. I saw you tried 132/4N but didn't read if you have you tried 138/2N or 1N?

Klxster, If his his top end is running well with a DJ138 at 2k feet, wouldn't that rule out MAJ issues? That would mean his bike's top end is running in the same known config as you tested at sea level: DJ140 main. Could it be a worn needle jet or main jet holder letting in too much fuel in the mid range mostly?

Sorry for long post and repeating, just sharing my thoughts. Good luck.

cheers.

 

I just don't know what's left to troubleshoot to be honest...

The carb is sitting right next to me and I can measure anything and check anything that's needed.

The needle jet is not worn on the collar or elsewhere. It's round - checked with a micrometer.

 

pwjm, have you entertained the idea of installing a TM36-68 on your bike? The TM is extremely tunable, and most of the hard work has been done in that venue already. Because you have a selection of needles, needle jets, main air jets, idles air jets, etc., there's practically no way you couldn't attain perfection. On the "why" of your bike not running like someone else's bike at your altitude with the same setup...there are different nuances in different bikes that can affect this, without the bike being "broken". I'm not trying to "sell" you on the idea of a TM, but apparently you're a fairly discriminating owner who wants an acceptable level of perfection.