Heres some help for poor low end preformance

Discussion specific to the 1995 - 2006 KDX200 (H Series) and 1995 - 2005 KDX220R (A Series) models sold in the USA
bikeman2502001
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Heres some help for poor low end preformance

Post by bikeman2502001 » 02:13 pm Aug 21 2020

As many of us have complained about loosing too much low end with the bigger carb mod I decided to take this head on and figure something out and this is what i figured out so far. The culprit that#$$%^&** #5 slide. We have had to go to very lean needle setting to compensate for the Ton of extra fuel poured in by the severely high vacuum of the number 5 slide. Its no secret that when a 2 stroke is jetted too lean they just dont pull like when givin a slightly richer setting. In an earlier post i said that the 7 slide was a huge bog dog I was wrong i just didnt take it to the next level and re administer more fuel back into it. This is a total reprogramming of the carburetor And you must throw all concepts of what you know and have learned from jetting with the 5 slide as the carburetor is now metering the fuel in a completely new and way more controlled fashion than before. The first thing you will notice when starting the bike is the idle will be way to high even thought you never moved the adjuster now the idle is controlled by the pilot jet Gone is that pesky 1/4 throttle wishwashiness we all hated.Idle quality is much better now. The midrange is now controlled in a much higher fashion you can now richen it quite a bit and its spot on thats exactly where our power went to lean of needle position. and the main will be the same. If this is a computer you just killed a very nasty virus and in stall a new operating system. I rode the bike for hours at the woods and could find little fault with this new set up. There no genius in this new setting as my both my YZ and the 13 ktm carburetor came with #7 slides in them so i knew the answer had to be there and is is Here are the new settings With the 7 slide yes they are wayyyy different that is a good thing as it addresses exactly what we were complaining about. This at sea level
7 slide
Stock needle in the 4th position
42 pilot
155 main
If those blingy reed cages cost 150 this is worth 250 but the slide only cost 60 bucks shipped on ebay you will need the slide for the PWK 33-35 carburetor
here is a picture of the two slides and the difference the left is stock the right is 7 Be careful not to go way lean on the pilot jet as before as on high speed decels the fuel comes from the pilot all that extra fuel is gone ENJOY
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bikeman2502001
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Re: Heres some help for poor low end preformance

Post by bikeman2502001 » 04:17 pm Aug 21 2020

Air screw 2 turns out

bikeman2502001
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Re: Heres some help for poor low end preformance

Post by bikeman2502001 » 07:19 pm Aug 21 2020

Jeff also sells a torque ring that goes between the pipe and cylinder that helps low end at only a cost of a couple hundred RPMs off the top there like 7 dollars If Jeff says it works it works he really is a no nonsense kind of guy

kdxdazz
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Re: Heres some help for poor low end preformance

Post by kdxdazz » 04:01 pm Aug 23 2020

Good write up and completely agree, I tried forever tuning with the number 5 slide, I ground it to a 6, it improved, then to a 7, it improved again, I stopped at 7.5
The slide, pilot jet and straight diameter of the needle are all. Interlinked at low rpm
1999 KDX220SR (KDX220-B5)

bikeman2502001
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Re: Heres some help for poor low end preformance

Post by bikeman2502001 » 05:27 pm Aug 23 2020

The Yz guys are swearing by the #8 slide and I believe they only go to 9 Im not completely sure yet but it looks like i might be getting a little better mileage by the looks of my gas tank. There really is alot of unmetered fuel going in there with the #5 now the needle or metering rod is in control like it is supposed to be

bikeman2502001
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Re: Heres some help for poor low end preformance

Post by bikeman2502001 » 05:30 pm Aug 23 2020

you must be a miracle worker if you can grind one of these slides correctly we used to do it in the old days but this one looks much too difficult for me I just bought the correct one

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Re: Heres some help for poor low end preformance

Post by KDXGarage » 10:05 pm Aug 23 2020

About 15 years ago, RB was cutting them for $15.
Thank you for participating on kdxrider.net. :bravo:
To post pictures from a device: viewtopic.php?f=88&t=24128

kdxdazz
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Re: Heres some help for poor low end preformance

Post by kdxdazz » 04:38 am Aug 24 2020

bikeman2502001 wrote:
05:30 pm Aug 23 2020
you must be a miracle worker if you can grind one of these slides correctly we used to do it in the old days but this one looks much too difficult for me I just bought the correct one
It's not that difficult at all, lots of info on the Internet about how to cut them, the numbers reference millimetres so it's just a matter of scribing a line and cutting, I used a stone then finished off with a file
1999 KDX220SR (KDX220-B5)

bikeman2502001
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Re: Heres some help for poor low end preformance

Post by bikeman2502001 » 05:54 am Aug 24 2020

I now am very curious that this might be at the core of the RB carb as it might very well the smoking gun, If any one has the Rb carb if you dont mind the next time you have your carb off would you mind measuring the slide cutaway its in millimetres It might say 5 on it but it might not be a true 5

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Re: Heres some help for poor low end preformance

Post by kdxdazz » 05:28 pm Aug 24 2020

bikeman2502001 wrote:
05:54 am Aug 24 2020
I now am very curious that this might be at the core of the RB carb as it might very well the smoking gun, If any one has the Rb carb if you dont mind the next time you have your carb off would you mind measuring the slide cutaway its in millimetres It might say 5 on it but it might not be a true 5
It's a seven, I also have the rb carb
1999 KDX220SR (KDX220-B5)

mobile chernobyl
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Re: Heres some help for poor low end preformance

Post by mobile chernobyl » 05:43 pm Aug 24 2020

Hmm. My airstriker 35 came with a 4.5 slide - it looks like there's some performance left on the table with the jump up to a 7. I would be keen on trying to grind this - I have my old PWK33 slide to practice on!

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Re: Heres some help for poor low end preformance

Post by bikeman2502001 » 07:11 am Aug 25 2020

If you mess up on that one ill give you my 5 lol

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Re: Heres some help for poor low end preformance

Post by oldmankdx69 » 06:15 pm Aug 25 2020

:grin: Hey kdxdazz, how is the listing for cutting a slide on the internet. I'm having a hard time finding one. I have a AS 35 with a 4.5 slide and would like to see what a 7 would do for me. Tried to buy one from jetsrus, but they don't carry one for a 35. All minfo is greatly appreciated. :grin:

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Re: Heres some help for poor low end preformance

Post by bikeman2502001 » 11:52 am Aug 26 2020

If you decide to buy a new one Sudco carburetors always has everything you will ever need I bought mine off Ebay

oldmankdx69
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Re: Heres some help for poor low end preformance

Post by oldmankdx69 » 01:03 pm Aug 26 2020

Just bought a new #7 slide from Sudco. We'll see if this solves my problem, hope so. May be a while before I get a chance to see, but will give report when I can. :grin:

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Re: Heres some help for poor low end preformance

Post by C George » 03:42 am Sep 10 2020

Am I correct as a general statement that the more one mods a 2 stroke and creates higher compression / intake vacume , the more necessary the leaning of the low speed circuit is
????
05 KDX-220R / 06 KDX-225R / Maxima 927 / Millenium Tech / Ron Black / PC , FMF / Many 220 engine mods / 40 + yrs. of riding dirt bikes 🤟🤟

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Re: Heres some help for poor low end preformance

Post by bufftester » 04:23 pm Sep 10 2020

I think basically that is a correct generalization, but also of note is that the more you mod a 2T the more important good porting/mapping becomes. Jetting is a fairly objective process (as long as your carb is in good working condition) that has limits. To move beyond them into more performance porting, pipe design, combustion chamber design all have room for tinkering. Seems these days not a lot of focus in the motorcycle world on 2T performance apart from implementing FI is done. But if you go look in the snowmobile world, 2T design has been pressing on, lots of good info on 2T performance improvement that can be transferred. Of course, 99% of the riding public never needs to go that far.

bikeman2502001
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Re: Heres some help for poor low end preformance

Post by bikeman2502001 » 08:21 pm Sep 13 2020

This is not just a high performance mod as the ever popular RB carb has this slide as per kdxdazz has stated
This cleans up that foul spot at 1/4 throttle as ive been reading post from many 2stroke riders in the mid 90 thru the early 2000s with the #5 slide dozens and dozens of complaints and this fixes that
Todays 2strokes already come with # 7s if you want to be totally persnikity about the slide selection Eric Gorr recommends a #8 in the summer and A #7 for the winter For my yz is I now have quite of ride time with the new slide and its win win all the way any 2 stroke That i buy with a #5 with ll be changed immediately this is worth way more than 60 dollars the bike has way better idle quality runs much cleaner the only change i made was to go back up to a 160 main this is a winner for everyone That is looking to make their bike run as good as they can changing just the needle only makes it a little less terrible

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Re: Heres some help for poor low end preformance

Post by kdxdazz » 06:05 pm Sep 15 2020

C George wrote:
03:42 am Sep 10 2020
Am I correct as a general statement that the more one mods a 2 stroke and creates higher compression / intake vacume , the more necessary the leaning of the low speed circuit is
????
I can say fairly confidently the more you modify the airbox the more you will have to lean the low speed circuit as the low end will become more inefficient, just as the opposite occurs, when you open the airbox the richer the top end needs to be, also the same with 4 strokes, the yzf runs leaner pilots than the WR series
1999 KDX220SR (KDX220-B5)

bikeman2502001
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Re: Heres some help for poor low end preformance

Post by bikeman2502001 » 02:35 pm Nov 14 2020

Heres an update on this mod after several hundred miles under the same conditions not only is the jetting issues completely gone I am getting considerably better mileage much better than 10 mpg before remember this is how the new 2 strokes are coming from the factory now the # 5 was commonly used a decade ago in many 2 strokes and every one was complaining about it then
Have a great day

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