Yep, it's on the list for sure.

Planning on doing the 351 - was going to do it this winter, but I hardly got to ride this season at all so maybe next winter and getting used to tuning the TM36-68 would be a good break in on the stock bore... even if the carb is a bit big for that application.

I feel like that'd be giving up on this issue though. I'm not the only user that's experiencing it (snowdrifter), so if we can figure it out, it might save someone else some trouble down the road.

Also, the TM36-68 is well over 400 dollars CAD right now with the exchange rate, that's a pretty hefty investment.

 

Yeah, the price is a pain, but this is one of those areas where a problematic CVK often remains a problematic CVK. I had one on an '86 KLR600 that was my wife's that refused remedy. And it wasn't like I wasn't familiar with the carb, because I had the identical carb on my '85 KLR600 at the same time. Swap the carbs, and the problem went with the carb to the other bike. I swapped critical internal parts between the carbs with no solution...diaphragm/slide, float, etc. I saw this occasionally with other CVK's on other models when I worked at a shop. I sometimes wonder if it's a casting issue or something. When they work, they work just fine, but I think a troublesome one is harder to troubleshoot than a non-CV carb.

 

Why is it different....
For one thing, everyone throws around their jet size... 132 this and 128 that. Well, you can't judge a jet size by the number, there are 2 or 3 manf and a 132 from Kiehn is not the same as a 132 DJ.
For second thing, the slide on the carb is run by vacum & spring. Ever measure the spring load? Well then if the spring is weak the slide is going to rise higher at all engine rpms.
I rode yesterday, at times my bike was missing in mid range, at times it wasn't. I'm blaming it on old gas and moving on down the road.

 

Would this be the right Carb?

Mikuni 36mm Accelerator Pump Flat Slide Performance Carburetor TM36 68 | eBay

 

Looks like the correct one to me by pic and description. That's an excellent price. Pure cost a couple or three years ago for me through my old bike shop was about $235.

 

In almost every case, the jet sizes are according to the dynojet products. Typically denoted with a "DJ" in front.

You're right that different brands have different and non-corresponding sizes and it's something I'm aware of.

I've tried the stock spring and the DJ spring (which is a shorter, weaker spring), neither seemed to make any difference. I've also played with the vacuum relief hole in the bottom of the slide by drilling it to 7/64'ths, sealing the hole and re-drilling to the stock size or smaller. Again, no real difference to be had.

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:

Top left of the carb oulets: 20150216_133319.jpg Photo by CASTIDGE | Photobucket - though I don't think this outlet is really a factor unless the plunger is pullet out as the majority of the plunger "barrel" blocks that hole

 

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....

 

Whoa! I have the same just not as severe. That is way more obvious than mine. My bike just seems to pause and then it's like a very mild 2T hit and off we go.
Only difference, since I noticed it, is the season/temps and a cleaner air filter.
My bike was running much better in the cold...I think I need summer and winter jetting.
Hope you figure it out.

 

That's a good way to describe it, while sputtering through the flat spot I'm just waiting for the 2T hit.



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.

 

I knew the bikes were basically unrideable in the stricken RPM range - but seeing/hearing it, makes a big impact.. We've got to get to the bottom of this..