*Edit- Ive resolved the problem, though I dont know exactly what caused it. 1N works now with the K148 main, no more issues.

Just a quick post on the differences Ive experienced with N1TC tuning using a K148 main jet in the past couple days.

2N: Bike seemed to run good through the range, low end seemed a bit weak, but no apparent rich spots, power comes on hard somewhere around 6500 rpm. Thought maybe was a bit lean down low, so decided to try 3N.

3N: Bike ran OK at first, low end power did not seem to benefit though. After warm up, midrange way too rich. At certain RPM, say about 3000 or so, wicking the throttle to 3/4 to wide open caused the bike to sputter and bog-- and it would not recover from this rich condition until you let off the throttle and let it rev slow with the clutch in (apparently drying off the plug!). After doing this, you could get up to the top end my a more gradual rolling of the throttle. Bottom line: still way to rich for 35' ASL, 95% humidity and 88F Louisiana days!

1N: Decided to see if my lack of low end was due to rich condition even at 2N. I almost couldnt believe after going to 1N the bike felt like a Honda 110 three wheeler--ZERO power. Very weak acceleration, bike would not rev over about 6500 in 5th gear, even less in 6th! Could not get bike over 50MPH! Way too little fuel, not enough to feed engine--even at WOT. Its like the main jet was never allowed to even open up! Very strange that one clip position could do this-- but everything was right on when I opened the carb back to re-set the clip to 2N. Its almost like the bike was being powered only by the pilot jet a small part of the needle.

Anyway, moral of the story is-- there is a massive fueling difference between 1,2,and 3 clip positions on N1TC needle (with stock KLX250 needle jet) when using larger main jets. Not sure how much difference with stock or smaller MJs, but I would assume that if 1N doesnt let enough fuel with a K148 MJ, there no way its going to with anything smaller.

The joys of fuel circuit tuning...

 

I'm running the N1TC - 2N with a k152 main and the standard spring/slide. As far as I can tell, by doing plug chops, it's pretty much spot on for my setup. You could always try a washer under the clip to raise 1/2 a notch

 

Allright-- so I got the needle moved back to 2N the other day and buttoned everything up for a real world test this afternoon-- a "ride it like you stole it" session, if you will.

So to be clear- this is what I was running--

Intake: lidless, screenless, properly oiled Uni 2 stage filter

Carb: N1TC, 2nd notch from top (2N), stock 250s needle jet, drilled slide (7/64), stock slide spring, Keihin #148 main, Keihin #40 pilot, Kouba screw 2 turns out

Exhaust: DG O-Series slip on, no baffle, stock header (LOUD SOB)


Things started good enough, bike fired right up, seemed to pull well in the yard, etc. Let it idle about 5 min whilst I got my stuff together, kissed the wife and kids bye, etc.

Took off down the road and the thing rips, really pulls hard, starting at about 6000 RPM. Rode about 6 miles to the first decent looking trail, jumped on it.

While on the trail, I noticed the low end doing some strange things-- wicking the throttle from anywhere under about 5500 RPM produced what I can only describe as a rich stutter/bog-- similar to what I experienced at 3N last week. Only difference is that it wasnt as bad-- the motor would recover from the stutter after a few seconds and would pull like an animal once it hit 6000 rpm. This stutter could be avoided by slowly rolling on the throttle, not going more than 1/4 or so until the revs got to 5500. This absolutely KILLED the low end, making it almost impossible to loft the front end up as it would stutter even in first if the throttle was wicked even to 1/2-- hell, it was even hard to clutch up.

I say this was a rich condition for 2 reasons - 1.) choke/richener lever pulled made it even worse. 2.) If I would chop the throttle while with stuttering/bogging was taking place, the bike would drop to a slow idle for a second or two before recovering, some times it would even die, but only when I was purposely chopping the throttle during the stutter to test.

I rode on about 50 miles+ of fire roads and forest pipeline trails and this condition stayed the same-- once you hit 6K rpm this thing felt like a ROCKET-- spinning the back tire in 4th and 5th under acceleration on the fire roads. Great top end - I could hit 60+ in no time at all, on dirt and grass trails. On the highway, I could do 84 sitting completely upright, got it to 89 in a tuck, which BTW is the fastest Ive been on the bike so far. Acceleration from 60 to 80 in top gear is very quick. I'd say the power I felt from 6K to 9K is at least on par with, and probably more than, my Cycle Works Racing built Mojave engine.

After riding for about 2.5 hours, Ive come down to two possible causes, and the one Im more inclined to believe is causing the problem is one that I cant easily fix.

Possible Cause #1: I think its the drilled slide. I broke down and drilled my slide the other day when going from a #138 to #148 main. I shouldnt have, I think. At #138, 2N, prior to the slide drill, I never had any problem wicking throttle from ANY rpm in ANY gear. If the drilled slide indeed allows the diaphram to lift more quickly, as is my understanding, I think too much fuel is being injected into the cylinder at too low an RPM and airflow for it to handle. This is similar to what happens with a non-CV round or flat slide carb when wicking throttle at low rpms, your engine will stutter or even cut out at times. This makes sense because in effect, what you are trying to accomplish by drilling the slide is to make it behave like a round or flat slide carb. This is terrible. Ive been thinking of ways to go back and the only one I can think of is to use JB weld or Bondo in the bleed hole to plug it up, and then drill it with a 3/32 bit or so.

Possible Cause #2: The #148 main is just allowing too much fuel to punch in too quickly when the needle /slide is snapped up, again probably due to the drilled bleed hole, but amplified by the larger main. Perhaps the smaller main would help here.

As I said before, I didnt experience this with the #138 main, 2N combo-- but again I didnt have the slide drilled. Unless someone has another idea-- this will be my first attempt to resolve this issue. The bike still pulls very hard with the #138-- as my memory serves, as good as the #148-- but the #148 was great today, the bike has a Ninja-like pull from 6K on. I know its not too much on the top end, but its killing my response from low to mids. I have to say that the best lows I can recall having on this bike was the #138, 2N, lidless, full exhaust. I drilled the slide when I went bigger, and my lows suffered, which is why I tried the 3N in the first place.

My last resort fix would be to go back to stock needle with a shim. I'd rather not do this but may have no recourse. Im really leaning toward that damned slide drilling being the cause of all this. My gut instinct was not to do it, but I figured it would be OK since so many do it and seem to be OK with it. Should have went with my gut...

 

About the initial post, the test at 2N was only a very quick run, less than 10 minutes or so, before I "decided" it seemed a bit lean at the bottom. The outside temp was also about 10deg cooler and probably less humid as well on this run than the long ride yesterday

I suspect that, had I taken it out for a real ride for longer, it may have had time to rear its head.

We'll see when I take it all back down again.

 

The needle jet itself doesnt have any aeration holes, so its probably fine. The emulsion tube that the main jet screws into could possibly have something clogging its aeration holes, thats a good idea, Ill try that. I'd be surprised though if it is clogged.

To clarify, I drove about 7 or 8 miles and as soon as I got on the trail, which was grassy and not dusty at all, I noticed as I slowed and started putting along.

When I take it down again Ill have to completely disassemble and go over with a fine tooth comb. I have checked the float level with a vinyl tube and it seemed to be OK last time I checked.

I too was very surprised at the complete lack of fuel at 1N. It wasnt just lean, it was completely starved. I found it very strange a single notch would do that. Thats one issue that I absolutely can not see the drilled slide affecting...

 

I've notice most of the cvk34 tuning revolves around WOT results vs. Real world off roading performance. I run a similar setup as you and find; dj132, DJ needle 3n, 2.25 turns out, enlarged slide hole, works the best, I will run a 128 in the summer. Anything richer than this, effects low rpm responsiveness, which is more critical than WOT performance in off road settings.
I'd start leaning out your main jet until you find a happy medium between responsiveness and max HP.
Good luck

 

This is a good point Matty. If I dont find any issues in the emulsion tube or float level, etc., and if 1N on the needle still doesnt work, I'll probably try to go back to the #138. The #138 is what I run in my CWR built Mojave (just a rebuild, not a big-bore), and the responsiveness and total range of power of that little green monster is just a thing of beauty. And thats using the stock needle with a shim under it. It runs so good, it puts a smile on my face just thinking about it.

If the problem is still there after the #138, Ill have to stick in the stock needle w/ shim. I def dont want to sacrifice properly running lows and mids for a barely noticable increase in top end. Even if the WOT AFR is not perfect at #138, if it still pulls as hard and the plug still looks good after a nice trek, Im OK with that.

 

Well, I really dont know what happened the first time out with the #148 and 1N, because I dropped to 1N tonight to help with the midrange overfueling and it worked great. No more sputtering/hesistation when wicking the throttle down low. No starvation either. 30 minute ride and it performed as good as Ive ever seen it.

Really good feeling lows, decent mids (absolutely no sputtering or detectable bog) and hard hitting top end. None of the fuel starvation, 50mph top speed the last time I used 1N. The only possible explanation, as KLXster alluded to before, for the previous starvation at 1N was that there was some kind of vacuum leak and/or the diaphragm was stuck and couldnt pull up to let the fuel up. As I said before, when I moved off of 1N back to 2N after experiencing the starvation problem, the diaphragm did not appear to be out of place or pinched.

In any case, Im extremely thankful I have a good working setup.

Now, the power on this bike still comes on really hard right at 6500 rpm, even with WOT say from 3000 rpm-- so this surge of power can only be explained by the dynamics/harmony/resonance of the intake and exhaust /cam setup. Its very , very obvious that something special happens at that rpm-- I checked it several times in several gears watching the tach and the surge ALWAYS comes on at the same time, ~6500 rpm.

My Mojaves simply do not do this, they have a much more even and smooth powerband, despite a nearly identical engine. Im getting more and more tempted to try the MCM.

 

Outstanding Josh !!

I'm really happy you got K148/N1TC@1N functioning as it should..

Our troubleshooting conversations was on PM - so the readers aren't aware..

BTW, from my testing, I would expect that you've gained around 2hp over your K138(≈DJ128) setup..

Ok, moving on...

This "hit" at 6500 rpm - are you talking a crazy "2 stroke-coming-on-the-pipe", tire spinning, "all hell breaking loose" kind of power leap, or just an increased pull on your arms? I.E. Will it pull a wheelie when "wicked WOT" from, say 6K in 1st?

While you are hitting max TRQ at that RPM, I'm curious about the abruptness of the "hit" . You see, I experienced that "hit" when I briefly ran my PC4 on the stock header. That hit never showed up with the DG-R nor with the full FMF system (Megabomb+PC4) and I want to compare experiences.

 

Well...I wouldnt go THAT ("all hell breaking loose") far , but it is similar to a mildly tuned 2 stroke coming on the pipe or if you are familiar with 4 cylinder bullet bike power, it reminds me of the hit of say, a CBR 600 when it comes into its powerband around 9000, albeit on a smaller scale (the KLX ain't no CBR ).

You ever rode a mildly tuned 2 stroke something like a Yamaha Blaster or a KDX 200? Its kind of like that-- its a very, very noticeable hit that happens-- and if you are in the right gear and turf, wheels will spin.

About the 1st gear, I can get it up as you describe. It will pop the wheel off the ground with no coaxing or clutch doing that, but to get it high enough to balance wheelie I just have to pull a little. No clutch needed though.