I have had 2 carbs on with different jetting and always have has MY misfire since I bought the bike. Its 6500 + RPM under light load. It was there when the bike was bone stock and still there a bigger jug and bigger carb later.

I fixed part of it by changing the gearing so the bike is not running at 6500 at indicated 62 mph. Now its less of a problem, bit I still think its ignition related.

Would anyone like to ride on the back and operate the O scope while I drive? This is the only way I can rule ignition out.

In college 30 years ago, my instructor said "Most carburetor problems are in the distributor" . I have found him to be right.

IDRIDER, stumble when real hot accompanied by a slight ping says too lean, but I can't tell from here.


David

 

Try to put your bike in neutral and rev it to 7k rpm. Keep it there and listen if it misfires. If it does then turn off the bike and do the similar test but with the voltage reg unplug. If it does not reproduce then the problem is not in the carb. I had thesame problem and kawasaki had to replace the whole wiring harness and spark plug connector. It fixed most of my problem but one sputter occasionally at 8k now but not above nor under.

I got very frustrated with this bike for 3months back and forth at the dealershipsss. They finally did all the work and am 3/4 happy with the bike now... They also replaced the digital speedometer as it stopped working after they replaced every electrical part of the bike.

Good luck!

 

IDRIDR, I didn't see what your airbox setup is in currently...mesh removed?...lid on/off?...snorkel? I'll bet a nickel that with a full header to match your muffler and all airbox mods, that even with a 250 stock jug you'll be at a 128 main and 3rd notch from top on the DJ needle. The bigger header pipe gives everyone the impression that this benefit is only at higher rpm, but I contend that low end is also dramatically increased and improved. I had the full header/muffler setup on my OEM 250 cylinder before going to the 300, and low end lugging power, with matching jetting of course, improved dramatically. Exhaust combinations are tricky, and I admit to not understanding all of the dynamics, but some weird jetting and power delivery issues are not uncommon with a mix/match setup of free flowing muffler and small OEM head pipes occasionally. It's not that there's no potential improvement with just the freer flowing muffler, but some jetting peculiarities are not uncommon. That skinny stock header is made to work with a fair amount of back pressure at the stock muffler. It's probably more of a challenge to match ideal jetting to the small header/high flow muffler setup than the matched setup of a bigger header/bigger muffler combo.j

Hey, I forgot about you having the Thermobob on your KLX. I wish I'd looked closer just to get an "in-person" view of one. I don't know...I'm still not convinced that the T-Bob is a big deal on our KLX's. You and I both have Vapor temp guages, so we can really see the temp swings in operation. The KLX has a very stable cooling system. I had several KLR600/650's, and they were all over the place in temp swings when you tried to ride them like a dirt bike. I can see the benefit on one of those. Still, I can't see the harm in one on a KLX, and it could be a real benefit on certain bikes.

 

Mesh is still there as I have a hard time believing that it has much potential to impede flow. Lid is off, but I plan on the larger snorkel. Twinair filter.

I wonder how important it is to 'match' the exhaust. If I get a powerbomb, do I also need to get the FMF muffler? Or full Muzzy setup? The HMF on there now was a used part from fleabay, and it may go back to fleabay if I need to match the exhaust parts.

The ThermoBob may not be a big deal. I really don't know, but like the concept of having the thermostat in the 'proper' location. I'd like to have ridden with the Vapor before installing the TBob to see how it fluctuates, but they went in at the same time. I ride a fair bit in cold weather and like the fact that it 'forces' the bike to warm up to proper operating temperatures within an easy mile from my house and holds a pretty consistent temperature, very rarely dropping below 176F and only going above 180 when air flow is limited (at a stop light, riding slow). The thermister is in the TBob bypass line, so it's always getting good flow pass of coolant directly from the engine.

 

Yeah, like I said...exhaust dynamics are both simple and complex, and I don't claim any all-knowing knowledge of it. I would agree that it would be best to match the muffler to the same company's recommended headpipe, but it's probably just as important to match higher flow to higher flow. Yours and my bike are so similar...at least before I added the 300 cylinder...that I'm sure the basic mods are going to yield the same results...and therefore the same jetting and performance. That slight, hot stumble you mention is jetting, and I'm just about positive of that. I just think there's a slight mismatch in your mods and resulting jetting that aren't playing well together.

I agree that on the screen mesh removal, that it won't be fully confirmed or denied on the possible performance benefits until someone does a dyno test on the same bike and same dyno on the same day to fully confirm anything. However, I'm not sure even that would totally do the trick. Subtleties in jetting and such could still be present without much noticeable influence on the dyno chart...or maybe not. I do know that my bike as a 250 and a 300 has what seems like perfect jetting and throttle response with the same jetting for both displacements with the same mods for both displacements. That surprised me a little. That day we rode Pritchett Canyon, I got 58 mpg. On a couple of other rides in Moab, I got 62 mpg. The worst I got was out at the Swell riding with those CO guys in some pretty harsh singletrack at 52 mpg. I'm thoroughly impressed with that in light of the power the bike puts out. I'm sure you'll get your stumble sorted out as you complete all the mods you're looking forward to doing. It's obvious you're diligent in your modding, so I know you'll accomplish that.

 

Agreed the stumble is jetting, and I think it's in the needle. Not many (if any) say the 2nd position on the needle is correct. I tried it, but now I don't think it's right. Back to 3rd.

My Moab mileage was right around 45 mpg and I've not had much if any better since mods. Had mileage in the 60's when stock. My attempts at leaning it out (main from 128 to 124, needle from 3rd to 2nd, pilot from 38 to 35) was primarily to see if mileage improved. It did, as I was pulling some 30 mpg tanks before. I'll put the needle back to 3rd position and plan to put the 15 counter sprocket on for a 15/49 setup (which is pretty close to a 13/42 setup) and see what that will do for mileage. Then I plan to play with the 124 vs. 128 main and see what happens. What is very clear is that the 38 pilot was too rich. The KLX300 with us at Moab has an even smaller pilot, I think a #32, installed by the local Kaw dealer during a power-up job.

 

09 Dynojet stage 2 per instructions snorkle pulled Uni filter, it really stumbles on the rev limiter but fine at all other rpms and no popping on decel. Actually I've never hit the limiter so I have no stumbles at all.

 

I have now developed this stumble also, but at lower rpms or when I let off of the throttle. It's the same jetting I did in 06. No problems til this year, may be due to the fact I havn't ridden much this year. I may try a carb clean. I have yet to try and fix. I will post any findings. Anyone else have this issue?