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rb carb mod with rev pipe

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Aug 2, 2003
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#1
Hi, I just sold my crf230 and bought a 03 kdx200 and must say I'm pretty impressed! The power in stock form is pretty impressive but I plan on modding it in a few months and my question is this...

I want more power throught the range because I ride alot of wide open throttle in upper gears and also ride in tight technical woods. If I did the rb carb mod mentioned in the hop up guide and added a rev pipe would this help? I want good low end to lug me up hills and get through tougher terrain. but I also want more topend because I ride alot of wider trails/fields too. My thinking is by doing the carb mod I will have better bottom end and tourqe and the rev pipe will help with the mid through top so Ill have a bike that will have good lowend traction that continues into a good mid and strong topend. I'm also plan on adding power reeds, removing airbox lid, and going up maybe 2 teeth on the back sprocket. By doing these mods will I accomplish what I want? Thanks for the time and sorry for the long post.
 
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#3
What was wrong with the crf230? Is it more akin to an xr than a cr?

'By doing these mods will I accomplish what I want?'

Guessing.....well, reading exactly what you say you're after...you will be happy with the 200 setup that way.

For the 'tight technical' part, you will be much happier with the DFII reed block with a low tension reed setting. Their reeds are the only way I could run the -30 in the woods and be happy with the bottom end.

imo and all that.

If you're looking for a place to dump some more $$, consider getting a modified airstryker vs: modifying the oem pwk. Much better mid-throttle pull and overall response. Ron can set you up with the whole shebang.

The best favor you will do for yourself and your riding enjoyment is to get the jetting right. Go to CDaves' site (linked in the 'every kdx rider should read..' thread stuck to the top of this forum) to get basic carb setup info.

Check 'new bike prep' while you're there. It will save you a whole lot of $$ in your near future!!

I'd like to hear about the 230, though........
 
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#5
You're kidding, right?

Honestly.....you couldn't possibly be serious?

For starters, check out (please!) the 'every kdx rider should read..' post stuck to the top of this forum. It links CDave's justkdx site so you can easily get there. Read what CDave says about the modification for starters.

Try some searches on this board. Persnickity, yes..but you should find plenty of input. I just tried "rb carb mod" and got kicked for a 'too short' input cuz search evidently doesn't recognize phrases.

You could check out the source of the matter HERE!

Ron's modification is one of the most discussed, most conversed about issues on this forum.
 
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#6
thnaks for the info. Also, I sold the crf230 because it just wasnt for me. Its not a race bike at all and its very similar to an xr200.
 

brentl

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#7
I do not ride KDX so I don't follow column. ( apparent isn't it)

I saw the post and it caught my interest.

I looked at the RB site.

Looks like this might be good for a MX bike with a big mid-hit and poor bottom response ???
 
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#8
The modification does improve bottom end response considerably. Besides being stronger, it's smoother.

Most any 'big hit' is something that can be tuned out jet-wise. Such a hit commonly comes from a carb circuit transition, one circuit being wrong the other being right. .....or closer to right, anyway.

Sounds like a thread for a forum that fits your bike and riding style. ;)
 
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Oct 22, 2003
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#9
I just put my KDX 220 back together this weekend. I put the RB Carb mod on it with Carbon Tech reeds and the FMF Rev Pipe. I started it up and let me tell you- it feels like it has the throttle response of a KX250. I won't be riding it until this coming weekend when I take it out to the desert, so I'll give a little report on it when I get back. Even though I hav'nt yet ridden it, my engines responds like a race motor whereas before it was lazy and would'nt rev out- and the cylinder and head are untouched! We'll see how she rides this Sunday (after church of coarse!)
 
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#10
Question; I have done extensive testing of different jetting combinations on my 200H1. Nothing I have done can seem to lean out the idle to 1/8 throttle area on my bike enough. Will the RB mod clean up this area of my carb (ie. change that area of operation in any way)?
 
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#11
Probably...but because of the jetting ron will put in it while he has it.

Does 'extensive jetting' include a 'C' or 'D' needle? That and a #7 slide will fix that 0-1/8 throttle right up. (Ron generally cuts the pwk slide to 7mm..oem is 5mm..as part of his modification.)

Or, re: 'Will the RB mod clean up this area of my carb?'

Yes.
 
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#12
CC, thanks for your reply. Yes, my testing included CCN, CEP, CEL, DCQ, and soon DCP, and DCN. I'm hoping that if I go with the modified carb I can move toward a richer and longer L1 (on the needle). Through 4 progressive modifications I have been moving toward the magic TV#7. I'm at at least a #6.5 right now (about 1/3 mm below #7 cutaway). My slide modifications seem to mainly effect 1/8 - 1/4 throttle with only a very slight effect below 1/8 throttle. The longer L1 seems to help the most below 1/8 but not enough, even with a very lean diameter. I've also tried pilots from 48 down to 38. When I improve the idle to 1/8 throttle problem, I also bring on a serious hesitation or flat spot when I "wick it" (as you say). This sounds insane, but the richer I go on the main, the better my flat spot/hesitation gets. I'm now at a 168 main and my WOT chops are almost perfect. As a matter of fact, my last WOT run had slightly stronger top end just off WOT than at WOT which suggests to me that I need to try a 170 main (69 degrees, 2600', 30% humidity). This is one of the reasons I'm considering the RB mod. I'm way outside what most folks are running, and yet very little smoke or spooge and very powerful.
 
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#13
If you want to visualize my hesitation/flat spot problem, take a look at the dyno charts on Canadian Daves web site........Notice how the power takes a huge dump at 4200-4300 RPMs?! That's what I'm trying to jet out of my power curve! When I manage to greatly minimize it, other problems begin to show up. So far I've been living with the lesser of the evils, but would sure like to perfect this setup. I like the bike too much to give up, and besides, I don't know what QUIT means! Tenacity is kinda built into me. My next line of thought is the RB mod and/or EG porting. I just wonder what some other riders on this forum did for a solution.
 
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#14
Happen to have a pic of a plug that is 'almost perfect' with a 168?

It's possible that one circuit not in the area you are working with is so far out of whack that trying to change the circuit where you have the problem is queered.

Your list of needles makes me wonder about that. A DCP for example....a 36.35 L1? And a 2.735 diameter seems way out in left field.

Seeing as the needles listed are quite a ways off (except for the CEL), that may be why your main is so far off...and why that main selection is having an effect further down the throttle opening chart.

If you start with this: '..but the richer I go on the main, the better my flat spot/hesitation gets,' and that flat spot is defined as, 'Nothing I have done can seem to lean out the idle to 1/8 throttle area,' then you know you're bass-ackwards somewheres.

The CEL (on 3/4) should be a decent enough place to start with a -7TV (less than seven, more than six.) A DEK in the same clips should work, too. Two clips different than the 'C's you mention...and considerably more rich on the diameter (smaller) to fit with the higher TV cut.

I'm saying I think you need to regroup..start from a known (works for others just fine) point and go from there. IF a 'known' starting point has big problems...find what's behind that before you go on another re-jetting spree.


.......I'd like to see that 'perfect' plug with a 168 main. If it is indeed perfect, there is something else rotten in 'ol denmark.
 
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#15
CC, I think something really is rotten in Denmark. Near perfect is a very light tan insulator (virtually white) with an ashen colored ring around the base of the insulator just under 1mm wide. Sorry, I didn't get a picture. I'll consider what you've suggested. ...from my notes; 38/155/CEL3/155/tv5=hesitation when I wick it. Same, with CEL4= hesitates, but less. Same, with CEL4/160=hesitation became just a flat spot. Same, with CEL5/160=less of a flat spot, but still there. Same, with CEL2/160="falls on its face" hesitation. These combinations all seemed a little lean on the pilot and blubbering rich when cruising on the straight section of the needle (around 1/8 throttle). 155 seemed way lean. Temps were 75 degrees with the 160 main jet tests, and 82 degrees with the 155 main jet tests. I didn't have any of my slide cuts done yet when I did these particular tests. What do you think would be a good next step?