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Questions and Answers about the best carb and Head mods available for the KDX.
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grump99
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Another satisfied customer!!!

Post by grump99 »

Just got my carb back from rb-designs. Only took a week to get back. Bolted it in and bike fired up 1st kick! Loads more power everywhere, very nice off-idle response. Well worth the money. Now I'm off to find that SSS! If you haven't done this mod yet, you should!
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canyncarvr
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Post by canyncarvr »

220 or 200?

Curious from a couple of standpoints. 200 riders have reported better luck finding it and liking it than 220 owners..although both have indeed found it AND liked it.

From the 220 standpoint, it seems the 220 head reconfiguration is an important piece of the puzzle.

Don't know why...but Mr. Black has said the 220 heads differ considerably as group from the 200 heads..which are considerably more consistent.

Maybe the SSS is less noticeably on a 220 that has NOT had a head cut/reconfigured.

Ski doesn't think much of the whole idea...but then he is running a race ported (and race-fueled) 220.

It's hard enough comparing Fuji aplles to Fuji apples, let alone just apples to apples, let alone apples to tangerines.

Look forward to hearing what your result is!!

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Indawoods
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Post by Indawoods »

I enjoy running at the SSS! And with the gripper AS.... it's all peaches and cream when you wanna just RUN!
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"People ate cows a thousand years ago for the same reason we eat them now. Cause they are easy to catch.We're not savages,we're just lazy. A cheetah could taste like chocolate heroin. But will never know. Those bastards are fast!!! "
grump99
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Post by grump99 »

I have a 200. Have a fmf torque pipe, 607 reeds, stock silencer, no lid. Took her for a spin yesterday. Set AS to 2 1/2 to start, adjusted by 1/32 increments. I think I found the SSS at 2 3/4 turns. I was riding up a steep bumpy hill and lost my momentum. I was in second gear and thought for sure I was gonna stall and have to restart on the hill. To my suprise however, by backing the throttle to about 1/4 and holding it there, the bike just tractored the rest of the way up in second gear! It would have never done that prior to the carb mod. Also at 2 3/4 the bike pulls down low a lot better than before. I found myself thinking I was in 3rd gear when I actually was in 4th. I could notice the difference in low end response with just a small movement of the AS, so I think I am pretty close to the SSS. It was like I was riding with the low end of an XR and the top end of a 2-stroke, very nice indeed. Also, the carb seems to have been jetted dead-on from Ron. It was sent back 150/40 CEK-3. My plug looked good even after a lot of putting around and no spooge at all. Couldn't be happier. Now I'm going to try moving the needle and maybe a DEK to see if I can make it even better, maybe a DF reed cage. Thanks so much!
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canyncarvr
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Post by canyncarvr »

To my suprise however, by backing the throttle to about 1/4 and holding it there, the bike just tractored the rest of the way up in second gear! It would have never done that prior to the carb mod. Also at 2 3/4 the bike pulls down low a lot better than before. I found myself thinking I was in 3rd gear when I actually was in 4th. I could notice the difference in low end response with just a small movement of the AS, so I think I am pretty close to the SSS.
Th'ar 'ya go!! :wink: It all sounds good...except fot the first part.

You were/are 'surprised' why? WHAT?? You doubted!!??

Pick your penance for that one! At least a couple trips 'round the beads!!


Isn't it a huge TREAT to ride your bike now? What you describe as the 1/4 throttle 2nd gear response fits to a 'T'. Being one gear 'off' is also perfectly descriptive of what the effect is.

Man...you are in for even more surprises!! DO try the CEK-4. Try the DEK just to see if you like it or not. Maybe you will, maybe you won't...you WILL know if you try it yourself.

The DF3? You WILL wonder what took you so long to get one.

Dang! Good report!! Well...of course it would stink if it WASN'T good..but that would only mean you did something wrong!! :wink: ..then we'd have to FIX IT! :blink:

That's great!

re: 'Couldn't be happier'

Sure you can! You'll find that out..........

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Post by grump99 »

Hehe, I am sorry I ever doubted! The penance you suggested sounds pretty fair punishment :mrgreen:. After I tinker with the needle position and pick up a DEK, my next step will be the DF-3. After that I might try a rev pipe just to see if I like it better and maybe a turbine core (although I like the quietness of the stocker). I have to admit, working on my bike was a little intimidating at 1st, but I have really learned to enjoy it. I can't wait to get the engine dialed in, so I can maybe start on a kx fork conversion. I am starting to understand what people mean when they use the word 'addiction' to describe their kdx. I just cant get enough :partyman: ! Thanks for the info!
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canyncarvr
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Post by canyncarvr »

Part of the fun of it all is the repeated, over and over even, refrain of, 'Wow. It's never run this GOOD before!!!'

You can find yourself saying that quite a bit if you tinker with your KDX.

I've been through that with multiple jet changes, a couple of carbs, pipes, SAs, dampers, forks, shock rebuilds, tires, fork preload changes, new seat covers, etc etc.

You mention a -30 pipe. It was a combination of things that convinced me to keep my -30 on no matter where I was riding. I used to change between a -30 and -35 depending on where I was going.

Between an RB modified carb, the DF2 (at the time..replaced a radvalve POS) and a premix oil change I found the -30 worked every bit as well on the bottom end of things as my -35 ever did.

Now...with all the changes since I'm sure the -35 would very likely work better than the -30 in the 'torque' category..but I sure don't need it. I'm much more likely to have a problem keeping the front end down than I am NOT having enough spit on the bottom. And I'm not talking about a high-rpm clutch feather that gets out of hand and loops the bike but just plain steep, too much traction and too little momentum.

..which is basically a rider error. Nothing wrong with the bike.

Here's yet another couple of things to think about. Consider a flywheel weight. From Steahly. Only one weight choice...8oz I think. You'll love it, too! Much easier to keep running on long downhills (brake touches won't kill the engine) and the added inertia can be used to your benefit.

For Christmas next year..ask Mr. Black (I mean ask him to send you one with the enclosed money order!) for an airstriker...sell your OEM PWK on some web auction place.

Find a (now out of production I think) Moose or Electrex lighting coil. Don't ask how (or why)...but it changes either the flux field shape or density and has the effect of giving you a better spark.

RickyStator I'm sure can rewind your light coil for the same effect.

All of this is off-topic..but it fits with the 'addiction' idea, 'eh?

Cheers!! :wink:

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grump99
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Post by grump99 »

Thanks for the info, its good to know that my bike has a lot of room to "grow" yet. I will keep posting as I try new stuff. Thanks again!
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Post by grump99 »

Took the bike out for a spin this afternoon. Temp dropped somewhat (mid 60's), and bike didnt run quite right. It would bog in 2nd gear with throttle wide open at low rpm only. I raised the needle to 4th clip (CEK) and response got crisper at low throttle opening but still had a bog at wot at low rpm. I then replaced the 150 main with a 152, and throttle response improved dramatically. I could nearly stall bike in 2nd gear, quickly roll (not jab) throttle wide open and bike would not bog, just pull! I was suprised at the difference such small changes made. A noticable hit has also developed, but it is very nice and controllable. I am tempted to bump the pilot to 42 or main to 155 to see it improves response further, but will leave as is for now.

I have a question regarding the low rpm throttle response. I'm not sure, but maybe I am expecting too much. When I am in 2nd gear on flat ground at walking speed (no throttle) and whip the throttle wide open very quickly, I get a gurgly hesitation (second or two) then strong acceleration. If I am in the same situation and quickly roll the throttle on to full (say over 0.5-1 second), I get no hesitation at all, just lots and lots of go. Is this where I should be, or I should I be looking to tune out that last bit of hesitation. To be honest, in my normal riding I never jab at the throttle like that, it almost seems like I am asking too much from the bike to respond that quickly to such a jab on the throttle at such a low rpm in 2nd gear.

Any thoughts are appreciated, feel free to chime in! Thanks.
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Post by RBD »

grump99,

Try adjusting the mixture screw for the best throttle response off the closed throttle position. Note! it only takes a small adjustment to make a big difference.

As sent with your carb instructions sheet:

Proper air mixture screw setting

Part of the modification of this carb is in the low speed circuitry. The mixture screw now becomes a great tuning device. Note: it only takes a very small tweak to make a big change. Only 1/16th of a turn will make a big difference. You will be able to keep your carb tuned for changing altitude and temps. Do not be afraid to play with it, have fun.

To obtain the proper air mixture screw setting is as follows;

You are not adjusting for the highest idle!

Start the engine and let it warm up to operating temp, with the bike in neutral blip the throttle from the closed position and see if the engine stumbles or stalls.

Adjust the mixture in one direction only a 1/16th turn at a time. Blip the throttle, if it improved turn it another 1/16th turn and blip it again. If the direction you first started with makes worse then turn it the other direction 1/16th turn at a time until you get the best response.

Next get on the bike and run it in gear with the engine idling and blip the throttle. Then try and adjust the mixture screw 1/16th turn in both different positions till you get the best acceleration off a closed throttle.

Finding the second sweet spot is similar, turn the screw out 2-1/2 turns and do the same fine tuning procedure as above. It’s a little tricky finding it and even a 1/16th turn can go right past it.

Sorry that it was not perfect right out of the box, I can only get you close. I hate this time of year as it is getting warmer in some parts of the country and colder or still cold in other parts......... Fine tuning maybe necessary.

Ron :rolleyes:
grump99
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Post by grump99 »

Thanks for taking the time to write. No need to apologize, the mod makes a huge difference, and was dead on out of the box when temps were 75+. I am delighted with the gains the mod provided. It makes riding the bike an absolute joy. Now that you mention it I completely forgot about adjusting the airscrew once the temps dropped, I am sure that will dial out any hesitation. Thanks for taking the time to chime in, I appreciate it. :mrgreen:
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