So here's the small problem. Occasionally at high speeds with the throttle open pretty wide, ( about 55-75 mph) the bike feels lilke it has a small burp or sputter. Almost as if the spark plug miss's once or the engine is mommentarily not getting enough fuel. It just comes and goes at will and I cant seem to replicate the problem when I want to. My battery is pretty much dead too and I have to push start it everytime. but I have no issues starting.
Also when I get a good steep wheelie ( 25-45 degrees) the throttle seems to bog down a bit. I have had the carb off recently to clean it because it sat for the winter but I put it together propperly and took it for a long ride and had no problems.

I guess I have a laundry list of potential problems but thought I might throw this out and see if anyone can help.

snorkel off, Dyno jet carb, a 300cc barrel and piston and holes drilled in the stock exhaust pipe.

 

The battery might be the problem. If the ignition isnt getting the proper voltage it could cause the sputter. It might actually be missing. Just go buy a battery. Kawasaki KLX250S (2006 - '10) Motorcycle Batteries - BigCrank.com

If the battery isnt the problem, maybe it just isnt getting enough fuel. Bigger main jet.

 

6500 rpm and up occasional miss. I think a lot of them do that. Mine does. I do not know the answer right now, but am working on it.

David

 

Same problem here...yet to figure it out

 

I have an oscilloscope I want to put on the ignition. It will record 40 pages of events and stop when I tell it to. It will record primary or secondary ignition. I want to find the problem. MY problem is attaching the tool and operating it while driving the bike and not crash.

Once the misfire happens, I have to tell it to stop recording so I can review it later. That is the tricky part.

One guy here said they unplugged the rectifier / regulator and the misfire went away. I have no idea, but it does seem to be spark related.

David

 

Though obviously not impossible, I think any throttle response problems with our KLX's is due to jetting rather than electrical. The ignition systems on these bikes are relatively bulletproof, and usually most ignition problems are manifested in total failure with no spark. Now that's not to say that one shouldn't run down all wiring connector integrity. The kill switch, spark plug cap, and ignition switch may be the weakest links in the whole system, and even they are quite reliable.

On the battery, I haven't studied our KLX electrical system in detail, but even though we have an alternator charging system, isn't the ignition/spark system still a magneto driven design?

Regardless, I'm betting on a fuel/air issue with most of the surging/sputtering issues that most riders encounter here. Almost all of these are accompanied by some form of modification. Unfortunately most of us are running just slightly different combinations of mods so that you just can't plug-and-play an exact jetting combination. However, I find the OEM CV carb to have a very large lattitude of satisfactory operation and performance with a good jetting combination. My carb is jetted ideally for my mods at a 1700' altitude, but my recent trip to Utah and New Mexico took me to well over 10,000' as it usually does with no issues whatsoever. While riding with IDRIDR at Moab, he complained of a very slight stumble just off of 1/8th throttle or so. We discussed needle position, main jet size, etc., but his bike isn't exactly modded like mine, so we don't have exacting comparisons to apply to each other's bikes. Though a bit of a hassle because of the somewhat difficulty of accessing the carb, it's just a matter of mixing and match jetting combinations until the right one is found.

One thing I'd start with before wrestling with jetting, however, is setting the fuel level to an exact and proper fuel level with the clear tube method and not using the static measurement of the float against the carb body. An improper fuel level can throw off all efforts to dial in the jetting.

 

As TNC mentioned above, when the bike was running hot during our recent Moab trip, it would irregularly (to regularly) stumble when bliping the throttle, usually when climbing a hill and trying to wheel up over an obstacle. It only happened when it was hot, and only at a low rpm condition trying to bump the front wheel up. When I say "only when hot" means after running for a while in slow, tough conditions, either descending or ascending the rough stuff with the coolant temp at 195F and higher. After discussing this with TNC...his answer was something like: "it's either rich or lean" ... I paid more attention and noticed lean pinging at lower throttle positions (around 1/8 to 1/4 throttle appx), but again, only when hot. I adjusted the kouba screw in and out at it made no difference to the stumble or pinging. My conclusion is that the needle is in a lean position and I need to go back to the 3rd clip from 2nd clip position (down from top). This change is pending, so I don't yet know if the issue will be resolved.

Regarding the OP's observations of stumble at high RPM, I noticed similar conditions with the 128 main jet and air box lid on (snorkel removed). I also had the needle clip in 3rd position and a 38 pilot jet and it was obviously rich at idle (even on a cold day, I could shut down the choke lever almost immediately after starting and drive off and black soot collected on the tail pipe and fender). I haven't noticed it with the 124 main jet (lid off, or lid on with snorkel removed), needle 2nd position and 35 stock pilot.

There's also been some comment this high-rpm stumbling is associated with the 2009+ bikes. Mine's an '06.

 

Wow..... mine doesnt stumble at all... until i hit rev limiter.

 

IDRIDR, apparently I missed the part about how your problem got worse when the bike was hot when we discussed this. That is usually a sign of richness at given point, but that doesn't jive with the pinging when hot symptom...at least not generally. After seeing your setup, I think I'd change out that stock head pipe to better match your aftermarket muffler. Not saying that's the exact problem here, but I think it would remove a possible oddball element in your mods. Also, did you drill the slide with your DJ mod?

And hey...did you take any pics of our rides? I only got one pic of that spot at the end of Pritchett Canyon with no action. Did you guys go out on BTR, and how did that end up? If you did a ride report, I missed it here.

 

TNC - the problem didn't get worse when it was hot...it only happened when it was hot. No issues when cold or warm. Never happened before, but I've never had the bike running this hot before (for you other readers, we were in the high 80's into the 90's at Moab, often into areas with little to no breeze and running in 1st or 2nd for a long time at low speed on tough terrain...and I have 13/49 gear setup...so the bike got warm enough for the fan to come on occasionally -- when the coolant temp exceeds 206F).

I'm planning on a better head pipe (probably the powerbomb), but I have a hard time thinking this is a headpipe issue when running at only around 2,500 rpm. I was going to save this until big jug, but maybe it will happen sooner.

Yes, the slide was drilled on the DJ mod. No clipping or tying together of the slider spring.

I have pics of our ride, just have been too busy to put the RR together. Pending...