Data Poll - RB Carb Mod for 200's

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canyncarvr

~SPONSOR~
Oct 14, 1999
4,005
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My carb has always taken a good deal more idle screw 'in' to idle well than before it was RBd.

I have less of that trouble with the DFII reedcage. I went from 1/2 or less on the airscrew to 1+ with the DFII.

I take 'won't idle' to mean it idles at real low rpm, but won't keep it up for too long? Likely you'll find the idle screw to seem pretty unresponsive..but turning it in a good bit will certainly help.

...might need to turn it out again for that cold-choke start process, though to keep the startup idle reasonable.

What fun! More to tweak!!
 
F

Fred T

Mi. Trail Riders
LIFETIME SPONSOR
Mar 23, 2001
5,272
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OK, thats simple enough to try. I agree that it seems to need more idle screw turn in than before RB'd. I should really probably inspect my Boyesen 607 reeds, they're a year old now.
 
J

Jim Crenca

LIFETIME SPONSOR
Mar 18, 2001
509
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Fred,
I'm sure you've checked all the obvious but I can't help but wonder if the problem is something other than the carb. It sounds like the bike runs fine when cold but has problems after it is hot. Will it run WFO when hot?
 
O

OLD-N-SLOW

Member
Nov 21, 2000
168
0
If it runs good cold but dies at idle when hot....sounds to rich on the low end to me. I would try opening the air screw some or going to a smaller pilot.
Maybe a larger needle dia. Try the screw first and see how far you have to go and that should tell you if more drastic measures are needed.
 
7

70 marlin

Mi. Trail Riders
LIFETIME SPONSOR
Aug 15, 2000
2,960
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Personally, I think the idle problem is just a trait of the bored carb on a 220? both my bikes act this way.
 
F

Fred T

Mi. Trail Riders
LIFETIME SPONSOR
Mar 23, 2001
5,272
2

Fast enough to change the color of my underwear in the whoops! :scream: Yes, it runs fine and idled better when it was cooler out and I ran a 42 pilot.

Maybe I'll try fisheys idea and throw in the CEJ#3 and a 35 pilot.
 
F

fishhead

die you sycophant !
LIFETIME SPONSOR
May 22, 2000
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70 marlin raises and interesting point. I found the plate caused some issues with the jetting that were not there when the plate is removed. I have experimented with multiple taper needles and feel they may be a viable option to the plated carb. Most provide a richer mixture at 1/4 throttle which improves throttle response. This prescriptive path provides a richer mixture rather than faster air velocity through the carb, thereby accomplishing the same thing without the added complexity of the plate. kx250 needle n3we yamaha n3ej or H and suzuki 250 needle n8rh are possibles ktm nozg, h, i, also possibles. Interestingly, all major manufactures of performance 2 strokes have migrated to multi taper needles in the past few years.

I found that jetting profiles that make a 250 a handful in the woods is pleasant enough on a kdx. yamaha n3ej-3 or 2 with a 45,48.50 pilot and 152 main would worth a good look.
 
P

penton32

Member
Jun 2, 2002
1
0
I have been dirtbike riding&racing for 30 years. It is rare to find good after market stuff that works real good.... But the RB carb mod on my 2001 KDX is GREAT !!! cleans-up the off idle and mid range problems with out hurting the top. Tell him all your bike mods and altitude and he will get your jetting close.
 
C

canyncarvr

~SPONSOR~
Oct 14, 1999
4,005
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Dan (acutemp) mentioned some time ago that he was going to do some dyno-whoppin' on trippple tapers as I recall. Haven't heard how that's going.

Maybe he got sidetracked by something unimportant...work...big bore kits for harleys..yanno, stuff that don't matter?;)

Frankly, I've been waiting for someone else to do the sorting out work.

Putting, say an NOZG in JD's spreadsheet shows the richer 1/4 throttle as fishhead says. Of more interest to me, though is the .01 larger diameter on the bottom. More lean right on the bottom and richer @ 1/4 would be great!

The 3/4 and up (the triple part) sure gets richer quicker!

While performance is nice..and pretty plugs after plug chops are, well, pretty...range is worth something, too. Summer riding in this area puts you in spots where if you don't get 70+ miles before reserve, you're in trouble.

I went on reserve @ 62 with my BEL setup. oops.

How about a dick tracy decoder ring chart for triple tapers? I haven't looked for specs on NOZG, N3WE and such. Anyone not lazy have a URL that has that info? (fishhead prolly has the chart photo'd in his not-cluttered but lived in space....;) )

The keihin site has a 'Jet Needles' entry, but it's not a link that actually GOES anywhere (as most of the others on the page do).
*****edit*****8-14-02

I'm sure this is elsewhere, but the search function ATT isn't working as it should (words joined with 'AND' aren't seen), and I've seen questions regarding this a couple of times recently. Towit: General contact info

The shop address is:

RB Designs
12025 NW Thompson rd.
Portland Or. 97229

Machinist name: Ron. E-mail address … rblack66@attbi.com

His website: http://www.rb-designs.com/


The cost is $165, including return shipping (as of 1-02 anyway), which includes: Needle change, slide modification to a #7 (stock is #5 on a '00 200), boring carb to 36mm (on a stock ’00 200 35mm PWK anyway), jet screen mod (casting clean-up), divider mod.

Note that some of these figures/specs may change from carb to carb.

Contact Ron for further info.
 
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W

wild willy

Member
Oct 15, 2002
1
0
wild willy here I have recently joined this forum. I have installed a 38tmx
mikuni it was a big job to squeeze it in to the bike but it was worth it. If
anybody has done this or has any questions write back.
 
C

canyncarvr

~SPONSOR~
Oct 14, 1999
4,005
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Welcome to the justkdx board.

Please do browse thru the faq which contains items as:

1. Do Not Post In The Wrong Forums


Can't tell from your post if you are referring to a kdx......or an RB carb at all?

Ron worked on your mikuni, perhaps?

This thread is used for the posting of information concerning the RB carb..something that can be fairly easily inferred by the title of the thread.

Completely unrelated, spurious and otherwise unapplicable posts don't help you get answers to questions, don't help others find pertinent information either.

While multiple posts are frowned upon also, you would get better results with a new thread.
 
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sledman

Member
Oct 23, 2002
160
0
I just purchased an '03 KDX 220. First mod will be the RB carb mod. I'm at 2500 feet altitude, and ride to 7500'. Mostly technical mountains trails.Any suggestions where to start with jetting? If I give this info to RB, will he jet the carb accordingly? This is my first 2 stroke dirt bike in 15 years.....been on an XR250 and 4-stroke ATV's for a while and got REAL bored.......Any advice appreciated.....
 
J

Jim Crenca

LIFETIME SPONSOR
Mar 18, 2001
509
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I'd let Ron "rough in" the jetting. He did my carb long before any of these threads, and after a phone call, sent me a different needle, main & pilot for improved response. I believe that he has worked with Dan (Acutemp) for current revised jetting and probably knows as much as anyone on this forum. The spread sheet from James Dean is also hopeful after you establish a baseline for your bike. Keep in mind that all KDX's do not jet the same; my 94 requires a much richer main than the norm.
 
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JSTUCKI

Member
Jul 8, 2002
28
0
My two cents: Listen to you guys, this carb mod sounds like a nightmare!
Put a pipe on, lower the needle one notch and go riding(2002 KDX220). All this jetting discussion clearly shows that this mod is more trouble than its worth!
 
S

sledman

Member
Oct 23, 2002
160
0
OK, but which pipe? Most of the guys here have FMF, the local dealer says they tested them all, and they like the Pro-circuit better. Remember, I'm riding technical stuff on narrow mountain trails, with lots of nasty climbs.....
And....I would want to enhance the bottom. That was what intrigued me about the RB designs carb mod. Sounds like it makes the bottom chug like a 4-stroke????
 
F

Fred T

Mi. Trail Riders
LIFETIME SPONSOR
Mar 23, 2001
5,272
2
The RB mod isn't pipe specific. It enhances the bikes performance regardless of which pipe you use. It just works and from what I read it will help you too.
 
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Fred T

Mi. Trail Riders
LIFETIME SPONSOR
Mar 23, 2001
5,272
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QUOTE:Put a pipe on, lower the needle one notch and go riding(2002 KDX220). All this jetting discussion clearly shows that this mod is more trouble than its worth!




Yeah, if jetting scares you that much, but we've only been trying to help with getting the folks with modded carbs jetted properly to start off. It has nothing to do with the carb mod - they just want to rejet their bikes because they have a different carb that's all. Your stocker will run like crap if not jetted right either, or you may be just too lazy to try to make it run as good as it can. You can be lazy with the RB mod too if you choose, but most of the people interested in spending $165 are willing to take a little time to get the most from the money they just spent. The bike is quite a bit stronger with the carb mod, at least speaking from experience with my 220. I thought the stocker jetted right was pretty strong too, but then I did mod my 220 and it was a really nice improvment.
 
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JSTUCKI

Member
Jul 8, 2002
28
0
I use the FMF Gnarly with the stock silencer and carb(needle lowered one notch) and love the bottom end power. Had also run the FMF pipe with their Turbine CoreII silencer and had better mid/high power but with alot more noise. Never fouled a plug.
 
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