Carbs Mods???

Questions and Answers about the best carb and Head mods available for the KDX.
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Carbs Mods???

Post by cmot »

I know the 220's were kind of choked in the carb area, but I see a lot of RB carb mod talk in posts and its one thing I have no clue as to what it does to performance and if it works on all kdx's?
Also can someone explain the need for extra vent tubes/or kits and what affect they have?
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Post by KDXGarage »

Check a post form dave04kdx from about 2 or 3 weeks ago. He asked the same question on the RB Designs carb mods.

Keihin makes an "Air Striker" version of the PWK that has a couple more vents. I am not sure how they help.
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Post by cmot »

OK cool, I read all the posts. Now to cheat, Has anyone went in to see what all RB did? Has anyone posted a pic of the devider? And still how does air vent kits work?
I tend to like to know why things work. Unlike Inda's credo (buy all the best parts and from there its just maintinence). Not that its a bad one. At all. But I tend to think I can improve on most anything made. (Not saying this is a fact, Many a good part has been tossed as ruined. But I've also had great successes to.)
Thanks....
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Post by Indawoods »

If you seen Ron's work I doubt you could do a better job... He has a pretty exspensive machining proccess and unless you own a machine shop setup for this type work... it would cost you a hell of a lot more to even get close to what he has accomplished for what he charges. I don't just go out and blindly buy parts... I first determine if they are needed because of some design improvement and if that will benefit me in the the way I ride. Not all aftermarket parts are right for everyone and their style.

The divider plate gives you the advantages of a small carb and a large one at the same time... this is a proven design... have you seen the "Power Now" setups? Same thing. But with Ron's work...the tolerances are so much closer. I think it would be hard to get those type of tolerances on your own.... not saying you couldn't do it... but is it worth going though all of the trouble and exspense if Ron can do it and get it back to you to bolt on in less than a week? :wink:
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Post by canyncarvr »

I wouldn't call the Power-Now things 'the same'. Big difference being upstream/downstream.

Well, I'm assuming you're talking about the upstream Power-Now plates which is all I've seen. Haven't bothered to look into anything 'new' from them.

I've had a couple of Ron's carbs. Considering the result (performance improvement), the tons of R&D that went into it (what kind of dyno do you have to test eleventy-dozen configurations of carb modification?) the beautiful work, all of the assistance that Ron freely gives to anyone who asks, and the fact that he's a downright good guy I have no interest in re-inventing this particular wheel.

IMO for sure...but copying someone elses work IS cheating for starters..beside the fact it just doesn't make any sense.


But...I don't swipe copyrighted music, either. :wink:

An RBD modified carb is bored and plated. The jet block heighth is changed on later model PWKs to keep them alike in jetting to earlier models. The pilot circuit is modified..don't know what that means exactly. I DO know it is turned into something that actually WORKS. The throttle valve is cut to 7mm.

Certainly you're more'n welcome to mess with your carb any way you like.

Good luck!

Oh...don't know where the idea came from, but Inda's supposed point of view being, 'Buy the best of everything..' is kind'a funny. Not even close...but funny. :wink:

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Post by skipro3 »

Power now has both upstream and downstream devider plates. At least I've seen ads for them.

I've followed a similar thread on buying the best of everything. My theory is buy the mods you think can help, try it and hope it covers up the extremely bad riding skills. If it doesn't hide the mod and never tell anyone. Good examples of this are the KX forks and the Scotts dampner. Bad examples are a garage full of tires thinking that I needed a hard terrain tire in rocky soil. Soft terrain tires rule in all conditions. Another bad example are a box full of bark busters that swivel, move, and don't stay in place to protect anything when subjected to a REAL crash. My lessons and new design will revolutionize bark busters everywhere. I'm going to be rich!!!! BwaaHaaaHaaaHaaa!!!!! :rolleyes:
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Post by igolfat8 »

First post here. A friend just bought an 04 220 (stock) and is a bit disappointed in the lack of top end. Can a carb mod fix that? Who is this Ron that modifies carbs and how do I contact him?
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Post by KDXer »

In a word..... "Yes"

He bores them out to a 36mm I believe and it enhances the top end greatly (as well as everywhere else in the rev range). Well from what I hear anyway...

http://www.rb-designs.com/kdx200-220.htm

OR EVEN BETTER STILL

http://www.rb-designs.com/KDX-PWK-AS.htm
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Post by Indawoods »

The head mod will help also.... Oh and uh... WELCOME! :wink:
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Post by igolfat8 »

Thanks for the quick response and the welcome. I raced competively for 17 years and now I am just an agressive trail rider. Owned and raced 9 KDX 200s. Now I putt around on a 300 EXC.
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Post by KDXGarage »

Welcome to the group. The 220 is designed more for low end performance, but with a few modifications can have more top end power.
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Post by canyncarvr »

re: friend that bought....

The 220 comes with a 33mm PWK Keihin, the 200 with a 35. That's why there is a considerable difference between the two bikes with a bored carb...the 220 starts out much smaller.

If the guy decides (correctly, I might add) to go the RB modified carb route, do consider sending the head in at the same time. Even for riding in Ohio (no el. to speak of) a properly set-up head will help...and the 220 is notorious for having heads of all shapes and sizes.

Don't forget to add a finger adjustable air-screw to the deal. It's in the 'Accessories' link on the RBD site.

BTW...you're familiar with the forever known issue of the 220 oem pistons coming apart? They've been doing it for years. Stock or not...it should come out. If you do much of any modification at all to a 220..first on the list should be piston replacement (Wiseco..another Pro-x is going to be same/same).

Another BTW...you prolly know this already, but....the 220 is not merely an oversized 200. They're two different animals. Instead of trying to turn a 220 into a 200, buying a 200 in the first place would work better.

...that more for the casual other-reader. Seeing as you've had nine of 'em..that's not news to you.

And neither one of 'em is a 300 punkin! :wink:

Oh...and uh...WELCOME!! :grin:

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Post by igolfat8 »

Hi Canyncarvr:
I have absolutely NO knowledge of 220's. I only have experience with 200's. I will pass this info on to my buddy.
Thanks again.,..
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Post by canyncarvr »

Well...a bit further rambling on the situation then (and this thread did start with a 220 subject line, so no [hijack][/hijack] tag required....;) )

As already said, the 220 piston issue has been around for years. The pistons are cast with some sharp edges that make them prone to cracking. It is often thought that only modified 220s are at risk...but there have been bone-stock 220s that have come apart, too.

The 'come apart' event may leave you needing only a top-end job. It can be much worse. Some riders have cracked the engine cases. There isn't any warning to it..it's not like it starts to rattle before it grenades..it just goes b-o-o-m!

Many more 220 riders have had no problem than have had problems. Guess that puts it under the Clint heading of, ''Ya feelin' lucky....???'

You having ridden 200s before, it may be of note that the 220 won't ever run like the 200...even with the restrictive carb problem rectified. The port timing is different between the two bikes. A 36mm carb will certainly help..and a carb modified as RBD does it will help more...but the 220 still won't be spankin' a 200 when the trail opens up a bit.

I'm sayin', don't think there is something wrong when his 220 doesn't run like your 200s did.

Cheers!

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Post by cmot »

Holy - moly How did the subject get so far off. I asked what the extra vent kits really do to help carbs. And what could I expect from a normal 90 to 94 KDX200 with a fmf fatty, carbon reeds, Jetted properly and running great could expect in extra performance from a RB setup.
From say... thats neat to OH MY GOD!!! :rolleyes:
Since most of you seem to have 220.s I didn't even know if your posts apply to older 200,s.
Inda's post answered partly and I've concluded its a extensive carb mod not to be taken lightly. And I directly quoted Indas credo from his profile. :grin:
This was not intended as a insult in any way.
Using other peoples performance ideas is a far cry from copyright infringement. :?
Everyone in racing had better come up with a completly different vehicle, no copies. Thats ridiculous.
Even if I had RB do my carb, before it ever went on I would have it apart to see what was done. Just to understand the concept out of curosity.
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Post by fuzzy »

Cmot: You won't even be able to see everything that was done....I understand your tinkering need(we all have one), but this is along the lines of porting/blueprinting. I don't even know how he get's in there and does the things he does.

The RB carb mod is not just for KDX's....He is a PWK modifying genious.....That 300exc mentioned above could benefit from the same work.

Back to the 220...I've ridden some that just plain spank. As CC mentioned this is rare due to the fact that they are timed 'wrong.' They produce lots of low, but lack on top even w/ a larger carb(considerable upgrade). Head work, a rev pipe, and delta force reed cage all work together to fix this problem. However, a port job is probalbly the most beneficial here.....In a way I disagree w/ CC's comment that the 200's are better. I've ridden 200's w/ all the goodies(bolt-on) and they just dont' compare to the well-modded 220's. One particular 220 w/ a 36mm unmodded carb, DF2, porting, and rev pipe would literally pull from 3rd off idle and pull 5th-6th(not me on it) gear wheelies. That bike impressed me immensely, and I've yet to ride a KDX that gave me that feeling since....

Never ridden an Eric Gorr 225...

My (stock) WR 250 has more torque than a 200 w/ all the goodies, but is no where near as 4-stroke like as the 220 mentioned above(and that bike had all the 2-T characteristics we all love too boot)...My WR has more on top than feasably concievable... :mrgreen:

In short...w/ some work I think you could possibly end up w/ a bike that you like better than your 200's. If your one that just keeps the bike rapped out all the time it makes me wonder why you never went the 200exc route??
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Post by Indawoods »

Try mine in the second sweet spot after I get the 12T! :lol:

And... nothing beat a KDX200! :shock: :wink:
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Post by canyncarvr »

I missed my saying '200s are better' part. That wasn't the intent of anything I said...which is why I didn't say it. :wink:

They are different is all. Example: Whether or not any bike pulls 5/6th gear wheelies has nothing to do with pretty much everything. I don't recall a time on any trail when I was really wishing I had that capability. Actually, I've gone to considerable time, trouble, effort and $$ to prevent my bike from pulling the front-end off the ground unless I WANT it to. I'm sure plenty of riders are perfectly happy with their 220s.

If it suits them, it tickles me.

re: 4-vent

Note the vent tubes are looped over the carb body? That's fairly obvious as to why. The purpose of a vent tube is to, indeed, vent. That means to allow the carb to be subject to atmospheric pressures in the worst of circumstances. After all, it is air pressure outside the carb that pushes fuel into the airstream. Obstruct that force..and your carb stops working.

Obstruction of that force will happen when the vent tubes are full of fuel. Thus:
Keihin website wrote:
Quad Vents: Eliminates post jump bog-down from fuel plugged vent passages.
Re: 'Also can someone explain the need for extra vent tubes/or kits and what affect they have?'

OkeyDokey?

Image


Note the airfoils on the intake bell? Thus the 'Air Striker' name.

..pic should show up eventually. It's coded right....he said hopefully... :neutral:
Last edited by canyncarvr on 02:54 pm Jun 15 2005, edited 3 times in total.

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Post by fuzzy »

Yeah, didn't mean to stir up that debate! :mrgreen: They both rock in different ways. Need to stop posting when I'm $hitfaced. :partyman:
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Post by canyncarvr »

[hijack!]Hey! I understand the 'Mine is better'n YOURS' point of view. :wink:

I've ridden 220s for a total of less than ten minutes..so my input as far as what's better is to be taken with a grain of salt (on the rim of a glass...with ice...with triple-sec and tekillya and a little Rose's Lime juice).

I know I'm happy with my bike when I can keep up with (even pass on rare occasion) a brand new state-of-the-art $6000+ 250cc bike ridden by a hugely superior rider.

I'm not pickin' a fight with anyone. ;) It is clearly 'Different strokes for different folks'..some folks like 20 more strokes than others!

All of this mod-this, mod-that routine is a process that will take years if you haven't already done it. I've used 'Great Stuff' that I thought was crap. There are still a lot of folks that think it's 'Great Stuff.' That's just fine! I'll wait for 'em at the top.

Take most any single item off my bike and its performance will suffer. They all work together...like they are supposed to. Put ON any single item I use..and it likely won't be terrifically impressive...if you even can tell a difference!

[/hijack]

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