Goofy CV carbs?...old fashioned slide carbs? I don't know. I looked on Thunderjet's site and I see plenty of high tech slide and CV carb applications listed there. Maybe looking beyond the pictures will help. This type of design has been around awhile and apparently works. Do you absolutely "need" a DAJ?...no. Do you absolutely "need" a TM34 pumper?...no. I have not tried one of these DAJ systems and probably won't, as I've had very good performance with the modded CV...at least for my use. It doesn't change the fact that the pumper and/or a DAJ might actually work and work quite well. Unless Thunderjet is being totally devious...and that's doubtful...they show applications for CV carbed bikes, including ours.

 

I'm sure you mean well but the "fact" that something "might" work is about as useless as **** on a boar. I looked for "our" application and did NOT find the KLX at all. Rather, it appears that we must order the ALL single cylinder four stroke kit which doesn't inspire confidence. I am aware that some of the listed applications may be for CV carbs but I don't know. What I do know is that our KLX isn't a listed application and that none of the shown installations are on CV carbs.

I'm starting to consider the slide carbs as old fashioned. I'm really pretty impressed with how well the CV works. This coming from a guy that has rebuilt and tuned a few double carb single cylinder XR engines.

Looks like nobody has a installed a DAJ on a KLX250 in this thread. I would love to see a write up about it. Something a little different.

 

Highbeam...they are listed for our bike and listed for every KLX250/300 setup from 1994-2009...DJ-109-AF & DJ-109-AY. While I would agree that there's probably not a dramatic difference in design between the different kits, that's probably because they're not reinventing the wheel with this device. And I had one of those '84 XR250R's, and the dual carb design was a PITA. Your take on cable pull slide carbs as perhaps being outdated is interesting, but I agree with you that the CV carb is still a very viable design for dual sports.

 

Your CV carb has a slide and butterfly in it just like KLX650C does. Butterfly is cable operated, slide is vacuum operated, doesn't take much vacuum to pull it up. The vacuum slide works smoother than a direct cable operated slide, that's why they're used on a majority of the streetbikes with carbs. I think a fair number of ATVs also use CV carbs, but not positive of that. So... Yes, it does work with CV carbs, my Nighthawk S had CV carbs and ran Dial-A-Jets.

Now it's addressed. Buy the Dial-A-Jet, I doubt you will be disappointed.

 

I turned my carb sideways to pull off the float bowl. I had perfect jetting first time. That's why I didn't buy brass, no screwing with three different mains, five needle clip settings, and the rest for me. I had it in within about an hour or so and it worked spot on immediately. Of course my old Nighthawk S did the same, so I expected that.

By the way, CV carbs don't compensate for altitude. They use the same needle/needle valve/main jet set up as a standard slide carburetor. I guarantee no CV carb will adjust for an opened up airbox, a big bore piston, and a full exhaust on it's own. The Dial-A-Jet did on my 650. I didn't have to touch it.

Of course until you try one you really won't know. You see, I've done both hard jetting and I've also used the DAJ. On a four stroke I will do the DAJ every time. Maybe if I was drag racing, road racing, flat tracking, or something like that I might do the brass, but not for general riding. It's just proven too easy.

 

The fact is my KLX650 is using the same kit as my friend's XT225. It works fine on both. There is no special trick to the design. It's pretty simple.

If you want to screw with taking your carb apart a lot, buy a Dyno Jet kit or just buy a hand full of brass from the Kaw shop. If you want good quick results without having to tear down a carb buy the Dial-A-Jet. That is coming NOT from someone who heard something from someone who knew someone, NOR is it from someone who just thnks that there's no other way than brass bits. ITS COMING FROM SOMEONE WHO HAS DONE BOTH HARD JETTING AND ALSO RUN A DIAL-A-JET FOR 12 YEARS WITH MODS FROM PULLING THE SNORKLE TO ADDING A BIG BORE AND PIPE.

If that's not enough, if you want to listen to those who have never used the part, do so. But while you're rejetting because it's not quite right you could have been riding. While you're jetting for altitude, you could have been riding. That simple. Seems ATV and snowmobile riders are far more open to new stuff that works than motorcycle guys are.

By the way, read the Motorcyclist and DirtBike! reviews. I'll bet it cost more for the print and testing than either magazine got from Thunder Products for advertising. In over 25 years I can't remember ever seeing one of their ads, so all that "they'll say anything for advertising money" is out the window.

 

Hmmm... i'm intrigued.

I might give this thing a whirl before i go pumper carb just for kicks, i can always install it on my 4 wheeler if I end up going pumper anyway.

Should i return to stock jetting or just drop down two main jet sizes or so ?

 

Depends on how much change there was from stock to where you are now. I know the instructions recommend dropping two sizes from proper jetting. I didn't do that though and still worked fine.

Actually I'd recommend you just call them up. Besides it's kind of neat to talk to the guy who knows the applications best. I think I talked with a guy named Phil, but I'm not positive of that. He can fill you in on all the workings and possible options as well as mounting methods. They now have what they call a Pro Mount, which wasn't around when I got my kit twelve years ago. I had an issue with the air boot not having enough room for their zip-tie style strap. I ended up drilling a mounting hole and filing off the raised edges on my stock air boot clamp to fit the body on it for a neat clean mount. My one regret is I mounted it inward at 11 o'clock when looking into the throat. I think now I should have done it at 1 o'clock so I could play with it a bit. But it's never been an issue so I've never changed it up.

Summary - call 'em at Thunder Products and get the word from the source. I really think you'll be pleased.

 

A few of my thoughts.

The lean makes more vacuum thing. I totally disagree.

To get the best idle, put a manifold vacuum gauge on the bike. Turn the idle mixture screw for the highest vacuum. Now do the same thing with a tach. You will find the mixture screw ends up at the same spot.

Sometimes for the best Idle, you need to go a little leaner on the mixture screw so when the slide pulls up or the accelerator pump gives it shot, the engine does not fall flat on its face. On cars in the 70s we would go for the "Lean best Idle" which would be set the idle for the fastest with the mixture screw(S) and a tach, then go leaner until it drops 50 RPM. This was for emissions more than anything, but it does make the engine run more stable.

More on the lean thing.

Your kit says to go 2 settings leaner than stock. Sure it does, it adds fuel all the time so it would be too rich if you JUST ADDED IT. Its that simple.

If your bike is too lean from the factory (meets emissions) which it should be, adding more fuel will make the bike run better. Almost any bike. Almost guaranteed.

More of MY opinion, If I am going to change the tuning of my bike be it pipe, intake, camshafts or what ever, I AM going to dial that carb in perfect. Each and every time I make a change.

More
David

 

Now for the high vacuum thing when the bike is leaner.

Still my opinion....

NO!

Max vacuum is achieved by the best running engine. Anything that messes with a best running engine changes the vacuum. Put a vacuum gauge on your engine. Turn the mixture screw and watch it change. Change the ignition timing and watch the vacuum change. Change just the Idle speed and see the vacuum change.

Any gas engine is an air pump. The more air you an pump through the engine for its size the better it works. If you restrict the exhaust enough, the engine will not have as much vacuum and will not run as well. This effect is bigger at higher RPM. SOME restriction is required or the valves can burn up. Some call it back pressure, I don't think that is the perfect term. The heat needs to be carried away along with the exhaust gas and sound waves.

The examples given of how you can hear the vacuum are not a good to me. You are measuring vacuum with your ear. My ear is not calibrated in inches of mercury. I don't really care what it sounds like. Put the proper gauge on it and give me some numbers.

I think the CV carb does adjust for altitude. When the air is thinner, the slide does not move as much. Not as much air (or thinner) is moving past the jets so it does not pick up as much fuel. Also all carbs work with atmospheric pressure as a base line. 14.7 psi on the fuel in the float bowl at sea level. As you go up, the pressure goes down.


Just to add, I have a "chip" on my BMW 1100. Its fuel injected and the chip has an accelerator pump option. That option is the best part of the gizmo. I am not totally against the fuel thing that started this whole thread. Its not a fix all either.

Happy Holidays to all

I need to go out and fire up my KLX because its 24*f out right now. I can't ride it in the snow, so I can just fire it up and go Brooom Brooom.

David