Data Poll - RB Carb Mod for 200's

Fred T · Jun 5, 2002

I'm from Michigan too! Here is the RB web address:
http://www.rb-designs.com/
The RB carb mod is a bored to 36MM carb with a divider plate added and some circuit modifications made to the stock KDX carb. It gives the bike much more snap and power at lower RPMs and if you have a 220 it lets it rev much more too. The 200 may rev a bit more too. not sure.

Your needle is the Stock needle and the other ones referenced in this and other threads refer to the Sudco model numbers. I think those are Kehein part numbers too. (?) Basically by changing the shape, taper, length of your needle and getting it in the right clip position can make your bike run much stronger and can manipulate the powerband to be the way it best suites you.

I have these changes on my bike and they really make a nice difference.

UPDATE:
I have added the 38 pilot jet now that weather reliably is above 60 degrees. Bike runs fine with that - and I feel my bike is jetted optimally for 65-70 degrees. I will need to either lower the needle one clip to #3 or move to a 150 main jet when the weather is in the 80's. Maybe both...I'll move the needle first next ride in the 80's. With my current jetting at 38-CEK#4-152 and A/S about 1 turn out it screams and pulls hard all through the throttle settings in 65-70 degfrees. 1200 ft altitude/ 93 pump gas - MX 2T @ 40:1

Hope this information is helpful.

Jim Crenca · Jun 5, 2002

Fred,

What was the cause of the idle problem?

Fred T · Jun 5, 2002

Jim
It's still not fixed totally but I don't have any stalling problems but I suspect that the pilot was a bit rich as the temps on Friday when I changed the jet was 80's and then on Sat/Sun they dropped to 65-70 and the bike ran and idled better. I was surprised how it reved especially from Sunday compared to Friday Night. 20 degrees difference in temp so I am thinking that it was rich for the warmer air and when it cooled off the jetting came to me. As I said I'll try a clip change first and then maybe a 150 main if I still need rev in warmer July weather.

Jim Crenca · Jun 6, 2002

Fred,

Man I'm lucky. My bike is not all that fussy even when the jetting is off. This spring I used my stock 70 degree, 400' above sea level, pump gas set up (165 main, 38 pilot, CEJ mid position, AS @ 3/4 turn out) and things were great. I then switched to VP C-12; WOT was a little rich and throttle response also felt rich and no better than with pump gas. The bike did pull better (more torque) and the brand new Dunlop 756 was spinning light mad although I don't fault the tire. I tried the same set-up at 2000 feet and throttle response felt a little slugish (although it was a tense ride over mud covered rocks for over 50 miles) but the thing was a torque monster. It had much less hit (like changing to a different needle taper) but was super forgiving when lugging up steep slopes in a gear higher than used last year (MX Tech suspension may have more to do with this than I give credit). Anyway, my bike runs really well. When it's jetted rich it runs differently but never badly. I rode a stock KLX last weekend and felt that while it may have more low rpm torque, the thing was a pig compared to a modified KDX! I'm not sure if I'm going to go to the trouble to fine tune for VP C12 as the $8 per gallon may not be worth it. Anybody encouraging the use of race gas (i.e. more hit or snapier response)?
PS - I've noticed that when the pilot and / or clip position is rich, the bike idles way faster when cold starting with choke; then rpm's drop considerably as the engine get warmer. I don't notice nearly this great a difference when jetting is crisp.

canyncarvr · Jun 7, 2002

High idle (runaway idle is closer to it) on a cold/choke start is indicative of a lean pilot. At least, I know this to be true with my bike, and fishhead has posted that situation/symptom in the past.

RTL · Jun 11, 2002

Okay, got in my first ride in a couple of weeks ago. New bike, new suspension, new carb, new everything. Ten years since last ride!

CEK 3, 152, 42, AS 1/2 turn out (as delivered from RB).

Rode jeep trails, rocky as heck, some single trail.

Bike ran great during the first part of the day, 2000 ft, 78 degrees. Carb allowed me to lug around perfectly, pulled great, very tractable and usable power delivery. Great woods performance. Since this was my first woods ride ever, I am having a hard time determining exactly how well the bike performed. I will need to get in some track test time to have something to compare to, but the bottom line is that the bike ran great in tight, rocky, rooty stuff. I had no problem controlling wheel spin! Yes, I was slow as a turtle, but the bike was hooking up.

However, I did notice that when I hit the wide open areas that I had a considerable amount of hesitation from 1/2 to 3/4 and the power seemed to fall flat early. Could just be me, but that is what it felt like. More to come, more seat time is required. :cool:

Also, my RT GV's worked great! A little harsh for the woods, but I'm thinking perfect for a groomed track, which is my first love.

SAGE, your rear shock work did just fine, no problems, felt good my man!

canyncarvr · Jun 12, 2002

Try CEK-4

Fred T · Jun 12, 2002

I'm going to try moving the CEK to #3 from #4 for my next ride. Pilot is 38, Main 152. Same other stuff as usual. I test rode it in the neighborhood and it seemed to have quicker response just off idle to like 1/4-3/8 throttle like it would bring the front tire up easier if needed in the tighter stuff but trail riding will tell the truth. What I might still need to do is go to a 150 main when weather is 80 degrees or above. Today it was cool and supposed to be about 70 degrees this weekend. I'll get back to ya'all.

Jim Crenca · Jun 13, 2002

Fred & CC,

Is the hit too agressive with the CEJ needle or do your bikes just run better with the CEK? I'm so happy with the CEJ I'm afraid (and time limited) to experiment as each ride is so precious time wise.

canyncarvr · Jun 13, 2002

I offed the 'c' series because it IS too aggressive (for me). It's lots of fun!..but a 70 mile hare scramble with the CEK would flat wear me out! My winter/spring riding area doesn't lend itself at all to a hard hitting bike. This summer, riding areas change..So I'll likely put the CEK back in..WITH my KG-30. Did that last year, anyway.

I've been using a BEL-2 for the last couple months. Like it much better. An EG (fine wire) plug helped quite a bit, too. Going to try an iridium, projected tip plug (a 'V' if I can get it. Thinks that the even FINER wire).

My bike has 'grown' SO much on the performance curve the past couple of months, it's incredible.

Oh, specifically, I HAVE a CEJ...but didn't ever test it. The CEK was pretty much on the edge of 'too small' diameter. I didn't think the 'J' was the direction to go (with the #7 TV).

It's tough to take the time to experiment when riding time is limited. I understand that. BUT...I've been happy with my bike in the past. If I'd just 'shut up and ride'...I'd not have gotten the bike to where it is now. And it's a WHOLE lot better than it was last fall. Just plain huge!!

You guys just GOTTA try a deltaforceII set to 'low' tension. Holy kaw!!

Fred T · Jun 13, 2002

JIm
I've not tried the CEJ yet because I suspect that it will be a bit rich off idle to 1/4 throttle. (According to James Deans sspread sheet. I've been working to tune out the richness down low and went to the 38 pilot with no problem. I like the hit of the cek, I'm used to it I guess. I understand riding time vs testing. I only make one change at a time so I can get it right. Next stop will be a leaner main@150 but only when I know it's going to be hot out. I'm not a good pplug reader but my "seat dyno" seems to work pretty good.

OLD-N-SLOW · Jun 14, 2002

Fred,
Funny how everyone that takes the time to test seems to come to the same (almost) setup. I'm at 35-150 cel-4 #5 slide. Would like to try a cem needle. Will lower the needle 1 now that sommers here. I'll bet your bikes running pretty good right now. I wish more people would listen. Spread the word.
Steve

Fred T · Jun 15, 2002

Yep, it ran good today. A bit cool (60) probably for the CEK #3 but I bet when it's hot out it will rip. It ran real clean at low throttle which was nice because we rode all day in the rain and mud. Lugging it over roots, logs, rocks and through slick trails was the hot ticket.

canyncarvr · Jun 18, 2002

Fred: If you haven't tried the CEK@4, do. I thought I'd settled on a CEK-3, cuz it worked SO well. JD mentioned that I might try it @ -4 to see how it worked. I was amazed at the change (amaze # 11dee4). Granted, it will likely wait for cooler temps..but if you get another 60º day, give it a shot (my last CEK-4 ride was with 38/150/#7TV, probably 10º cooler, though).

O&S: Yeah...funny how that works, 'eh?

Fred T · Jun 18, 2002

CC
It was at CEK #4 all early season and I just moved it to #3 because I thought it was going to be warm but a cold font moved in and it rained instead. I'm at 38/152/CEK #3/#7TV now hoping for more summer like weather. My next change will be to try a 150 main jet. (Once I am positive it will be 80 degrees.)

andrew · Jun 19, 2002

I don't understand how some of you blokes can run such lean jetting and get away with it! I'm seeing 152-150 mains and 38 pilots - YIKES!!
I know some of you have 220's that came with the smaller carb, but if you have the carb bored to 36mm, wouldn't you need to jet a bit richer??
heck, if I go leaner than 155/45 I seize the engine!!
Has your altitude got something to do with it? I didn't think it should make that much difference - not 3-4 sizes anyway!!

Cheers to y'all
<<oops, the dreaded swearword nazi got me !!>>

OLD-N-SLOW · Jun 19, 2002

Andrew,
Reread some, these settings are with the cel needle.
By the way, have you seized a motor by running to lean?
You almost never here of that any more now with water cooling and synthetic oil.

andrew · Jun 20, 2002

yes mate, I have (once). How come a different needle can let you go so lean? My understanding is that the needle has little effect at WOT, and if you're too lean that's where you'll find out!!

Those small jets might be OK on slow technical trails, but when you're giving the ol' girl a caning....well, I reckon y'all are too lean!!

G. Gearloose · Jun 20, 2002

Andrew,
The _ _ J, _ _K , _ _ L needles have markedly smaller diameter straight sections than the Kawi 1172-1174 needles, thus permitting much smaller pilot jets.

As for the main, some of these folk are at elevation, read the plug at the insulator base vs tip, etc

Or maybe your bike is like Jim's :D , or has an air leak, but 152-155 is likely the bulk of the distribution.

Describe your setup, perhaps someone can figure why...

70 marlin · Jun 20, 2002

you hit it Andrew! tight narley woods mostly. I do try to keep my main as large as I can. as you'd put it, "ol' girl a caning".

ochster · Jun 20, 2002

Just gone done building a fully modified 220 with the RB carb. I ended up settling on a CEJ, clip in the middle, 40 pilot, 152 main. This is with pump premium, MX2T 40:1, sea level to 1000ft. The transformation in this bikes personality is stagering. The power builds through the complete throttle range, no flat spots, and it will easily loft the front with a simple roll on.

acutemp · Jun 20, 2002

It's testing season again :confused: . I have finally got my bike back together and got a chance to get out for a couple of rides. I am breaking in a new top end so I stuck with my favorite setup from last year and it ran great. :) The only change was a switch in gas from Trick 110 to Sunocco purple with hp2 at 32/1. Settings were 36mm RB carb, 40 pilot,CEJ#3, 152 main, a/s at 1 turn out.
I have some new needles to try in both my 36mm and 39mm carbs and will post my results with them also.

Andrew,
The needles that are being used with these jets are also a different (steeper) taper than stock so they are richer at WOT. You might want to give these a try. If the sudco needles are not avalible try finding a honda item. A r1369-70
would be a good starting point close to the CEK-L.

--Dan

canyncarvr · Jun 20, 2002

Andrew:
All of us are quite a bit further up in elevation than you. Just take a look at a globe. Hold it so the letters make words (in most cases..NOT like ZBEYKWZRTYstan) and you can plainly see that 'we' are quite a bit further 'up' than are you.

That and the greatly condensed magnetic field up here will make jetting considerably different.

Actually, in the summer I run a KG-30 with an 1174L and 42-152. That's the ONLY combo I've ever run that shows a VERY pretty plug in every carb circuit. 150 would have been good to go, but a bit too skinny to suit me. Granted..it's 1173-5...and it's 35-7500'el. but it worked terrific!!

Ochster: What's the red thing? Looks honda-ish;) Looks new to me, and going back (only a few months) I don't see posts from you on CDave's forum.

Does this mean you're a convert to green?

andrew · Jun 22, 2002

Canyncarvr, of course!! Y'all are so much further up than us Aussies that it's a wonder you're not running 130 mainjets!

Hang on!! Maybe it's me that should be running a 170 main ?! Oh god, I'm soooo confused!!

BTW, I'm currently running a 45/155 with the stock needle in the middle. RAD valve, ported for top end, FMF rev pipe and Steahly flywheel weight.

For a while there I thought I may have had an airleak, but it was just that I needed new reeds. Runs like a dream once more!

Cheers to y'all. :cool:

ochster · Jun 25, 2002

canyncarvr, The red thingy, is Thumps handiwork. And yes, you could say it is Honda-ish by design.

I have a couple friends that compete on KDX's, and they wanted more. After watching all the bolleywho about the RB set up, I wanted to try it. The machine all done up, is a worthy contender. The motor actually proved to be the easy part of the equation. The suspension required major rework, and rebound adjustability.

Data Poll - RB Carb Mod for 200's

Fred T

Jim Crenca

Fred T

Jim Crenca

canyncarvr

RTL

canyncarvr

Fred T

Jim Crenca

canyncarvr

Fred T

OLD-N-SLOW

Fred T

canyncarvr

Fred T

andrew

OLD-N-SLOW

andrew

G. Gearloose

Pigment of ur imagination

70 marlin

ochster

acutemp

canyncarvr

andrew

ochster

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Data Poll - RB Carb Mod for 200's

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