Mid Range Sputter / Misfire - Input welcome
Senior Member
1st Gear Member
Joined: Oct 2013
Posts: 179
From: Mexico
Wow! It just seems to hang there in that rpm, like you paused a video jaja. Definitely something wrong. The second video seems "normal" rich behavior to me, with my limited experience in this matter.
PWJM, how bad is your bike compared to these videos?
PWJM, how bad is your bike compared to these videos?
Senior Member
Joined: Jun 2013
Posts: 3,317
From: North Texas
1st Gear Member
"When I started the bike today, I tried to pull away quickly before it had a chance to warm up at all and the symptoms seemed less severe, though still present. But within minutes it was back in full effect."
Well, if this IS a carb-only issue, then -
From: CV Carb Tuning Procedures
"NOTE: A rich problem gets worse as the engine heats up."
But in this case (a carb-only issue) your carb is overfueling with what would ordinarily be a pretty lean setup.. WHich is the same apparent possibility that PTSD has..OH.. I mean PWJM.. PTSD is what we are all gonna suffer from after we figure this nightmare out...
Well, if this IS a carb-only issue, then -
From: CV Carb Tuning Procedures
"NOTE: A rich problem gets worse as the engine heats up."
But in this case (a carb-only issue) your carb is overfueling with what would ordinarily be a pretty lean setup.. WHich is the same apparent possibility that PTSD has..OH.. I mean PWJM.. PTSD is what we are all gonna suffer from after we figure this nightmare out...
Last edited by Klxster; Jul 29, 2015 at 02:52 AM.
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Senior Member
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Joined: Mar 2015
Posts: 283
From: B.C. Canada 2000' ASL
Been busy for the last few days (did my first dual sport ride!) and trying to get caught up on this issue. Took the KLX for a quick spin after work and took some video of the flat spot:
First video is a WOT pull in 5th gear. It illustrates how slowly (if at all) the bike accelerates through the flat spot in higher gears. The video isn't fantastic, but the audio helps identify the problem area, from ~4K to 5.5K RPM. As soon as it gets over 5.5K, it cleans up and takes off.
Second video is a couple of quick pulls in 3rd gear. You can still hear the flat spot, but see how much faster it accelerates through and then cleans up.
Haven't had the opportunity to mess with any electrical components, though it looks like others may have tried that without success?
I may try to rig up the camera to record the slide in the carb while riding. I'm curious how the slide moves under load. To be continued....
First video is a WOT pull in 5th gear. It illustrates how slowly (if at all) the bike accelerates through the flat spot in higher gears. The video isn't fantastic, but the audio helps identify the problem area, from ~4K to 5.5K RPM. As soon as it gets over 5.5K, it cleans up and takes off.
Second video is a couple of quick pulls in 3rd gear. You can still hear the flat spot, but see how much faster it accelerates through and then cleans up.
Haven't had the opportunity to mess with any electrical components, though it looks like others may have tried that without success?
I may try to rig up the camera to record the slide in the carb while riding. I'm curious how the slide moves under load. To be continued....
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Senior Member
1st Gear Member
Joined: Mar 2015
Posts: 283
From: B.C. Canada 2000' ASL
but when I went to sea level the issue had all but disappeared...
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Joined: Mar 2013
Posts: 866
From: SE Asia
The vast majority of the forces lifting the slide are actually the big mouth in the bell of the carb. Here's a picture of another carb (not mine) for reference: http://i.ytimg.com/vi/ndHmI9flPCA/maxresdefault.jpg
You can see the mouth at the top of the inlet.
In relation to that opening, the vacuum draw over the slide is maybe 1/100'th the amount of force. Consider also that there is draw through the choke circuit on the outlet set of the carb that contributes:
Which yields more rev/vacuum and more slide lift. I'd bet the air inlet could be anywhere and the carb's performance would be the same, rather than lessened just because it's not facing a moving airstream.
Just block off the slide's vacuum hole and see how well the bike runs to find out
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Joined: Jun 2015
Posts: 21
From: Chilliwack B.C
pwjm. when your bike had my carb in it the issue disappeared. as I said then that this gives you a starting point to work from.
set your bike up with a dj 124 with needle at 2n,lid on( same as Mine). run the the bike and if it does not stutter anymore then move on to the next change( if it does stutter with this setup then maybe your carb has an issue because it worked with mine in). Change the main jet to a dj128, run the bike if all is ok, change the needle to 3n, run the bike. if again all is well then remove the air box lid. run the bike again. keep making these changes one at a time until you replicate the stutter, then undo the last change that caused it.. Forget about running rich or lean for now ,just find out where your bike runs its best.
set your bike up with a dj 124 with needle at 2n,lid on( same as Mine). run the the bike and if it does not stutter anymore then move on to the next change( if it does stutter with this setup then maybe your carb has an issue because it worked with mine in). Change the main jet to a dj128, run the bike if all is ok, change the needle to 3n, run the bike. if again all is well then remove the air box lid. run the bike again. keep making these changes one at a time until you replicate the stutter, then undo the last change that caused it.. Forget about running rich or lean for now ,just find out where your bike runs its best.
