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Looking into the newly released SmartCarb SC3 34mm, this carb very much appears that it will be a good fitment into the '95-'06 KDX200H & KDX220R chassis, unlike the completely non-fitting previous generation's SC2 36mm version, or even the older Lectron carb versions which are a poor fit (although they in fact can be run on the '95+ with mods/compromised mounting angle/stock reed cage only).
The intake spigot looks to be 1mm shy of the diameter of the PWK33/35 OEM KDX carbs, but I'd imagine this would still be quite workable and clamp down just fine into an OEM intake manifold boot with VForce4 or a Boyesen RAD Vapve intake coupler.

It also appears they will require the long body adapter (Same as the 34mm Lectron Billetron Pro Series 38 carbs do. This is optional with the purchase.
For $20 on their website, they do offer a 3D printed mock-up of these carbs for test fitting onto bikes which they have not yet verified fitment on.

https://smartcarb.com/product/32-34mm-s ... -3d-model/

With as frequent of requests they get for SmartCarb offerings to fit the KDX200/220 based on what they told me 1-2 years ago (they said at least once or twice a week they get a KDX owner contacting them wanting to buy a SmartCarb, but had nothing that'd fit the 95 & up KDX frames until now), I'd imagine at some point they are going to have a published fitment offering for our bikes, but for now, we can only wait and see. An inside connection told me that they were very much designed to fit the '95+-'06 KDX frames, as well as the 32 mm version which looks like it was designed to fit some other smaller enduro and trials type bikes. The 38mm & 30mm versions as well, which might make a very potent woods-modified KX112 SuperMini 2-stroke as well!





I think I'm going to pick up one of these this winter for a more Hard Enduro focused torque monster tractor engine build out of my spare 220 with a ported 70mm bored 223cc cylinder and a slightly modified KDX220SR head (come stock with much tighter squish clearance but a very wide squish band around 13.5 mm versus the Ron black carb at 9.5 mm which is close to stock but tighter squish clearance. I think I'll pair this with a stock pipe or Gnarly Woods pipe, & the SC3 34mm with its variable shaped Venturi should be a great carburetor for this engine as the low throttle opening area is much narrower since it is egg-shaped at the bottom, giving higher air velocity at low throttle for more low end torque and better throttle response when cracking the throttle open from lower/mid-RPM cruising position. In addition to that, I speculate it might be larger overall carburetor venturi bore area than a circular 34 mm carburetor bore, so it's likely it may flow every bit as much as a PWK 35 at wide open throttle, while having better throttle response down low than a PWK33.





These are a very advanced carburetor, and perhaps the best carb on the market as a whole now.
The Lectron Billetron Pro Series w/ Xcelerator metering rod is also a listed fitment for our bikes now. I was the first guinea pig for this after making connections with Matt Denecke who formerly worked at both electron and founded Apex cylinder heads, and now has his own company making prototype YZ400 2-stroke engines.
The Billetron Pro Series is an incredible carburetor that utilizes both the metering rod design and two supplemental thumbscrew adjustable jet circuits to make tuning a lot easier I need to change any brass parts.
The smart carb is even more advanced and has a few additional features, I believe they have some sort of spill proof design with a check valve so that no fuel will spill out when you lay the bike down on its side, as well as the advanced cloud venturi design I believe they call it, how it is narrower at the bottom for better air velocity and throttle response. Additionally, the Smart Carb delivers all of it's fuel off the metering rod instead of having one or two supplemental jets as the Lectrons and the XTNG (doesn't fit the KDX200H whatsoever) carbs do.
With the fuel across the entire range delivered solely off of the metering rod and no supplemental Jets to introduce larger less atomized fuel droplets like the standard carbs do, as well as no supplemental jet tubes that disrupt the laminar air flow through the Venturi bore, a smart carb with the proper metering rod and proper adjustment will deliver the most complete combustion and highest fuel efficiency possible out of any carburetor, surpassing that of fuel injection even. The Lectron Billetron Pro Series carbs have been said to outperform modern KTM fuel injection systems already... The Smart Carb when fully optimized promises to deliver even better.
I have a PWK33, Ron Black modified 36mm Keihin PWK 35 Air Striker Quad Vent with divider plate added, an old style legacy era Lectron 34mm Power Jet carb, & Lectron Billetron Pro Series. The RB'd PWK35 Air Striker and the Billetron Pro Series Xcelerator metering rod carb are my favorite out of those, but I believe this SmartCarb SC3 34mm will be right up there at the top as well alongside the Billetron Pro Series Xcelerator. I definitely would like to get one of these this winter and run it on the hard enduro engine build. I may even weld an O2 bung into my expansion chamber so that I can test air fuel ratios and attempt to perfectly optimize the metering rod tune.

A purple anodized SC3 34mm may very likely find its way home to one of my machines this next season, if not the green anodized version...



We've got TWO incredible options now for aftermarket carburetors thanks to these two good companies.

great info and cool bonus that they come in different colors!

I read some comments online about the anodized body versions. These SmartCarbs are all made in the USA, however, they were not happy with ANY anodizing company that they had tested here in the United States (they tried more than a few), and actually send the carb bodies to Europe to be anodized I believe in Germany currently, so the custom color requests take quite a while to be delivered due to this. Unless it is something they sell a lot of and may have stock in a certain carb size and color, it may take a good 4-5 weeks to get something back, assembled, and delivered.

All sounds great , my concern is the right metering rod being available, if no metering rod works then it's an expensive paperweight, only from my experience with the older style lectron trying to get it dialed in proved impossible, but a couple of years experience up my belt and the wideband O2 sensor means I might give it another go
I do like the smooth idle of the metering rod carb

kdxdazz wrote: 09:22 pm Oct 13 2025 All sounds great , my concern is the right metering rod being available, if no metering rod works then it's an expensive paperweight, only from my experience with the older style lectron trying to get it dialed in proved impossible, but a couple of years experience up my belt and the wideband O2 sensor means I might give it another go
I do like the smooth idle of the metering rod carb

100% my concern as well. I feel they definitely have the metering rods available, however, they are cost prohibitive to purchase several different metering rods to tune with,so you'd be stuck installing, testing & re-figuring richness vs leanness on various throttle positions, ordering another costly metering rod, waiting, installing and testing etc potentially going through a couple of rods before you're satisfied with having iseal exhaust gas temperature and AFR and ideal piston wash pattern (which only works with certain premix oils as I've noted, some are meant to burn extra clean and leave no carbon traces pattern on the piston crown, eliminating a very useful method of judging an ideal mixture for mid to upper throttle positions in the powerband).

I still feel the desire to buy one and get it set up for the ported 223cc cylinder and the KDX220SR head in order to have a very torquey responsive engine with primarily very strong low and mid-range grunt.

Given their "CloudForge" venturi design, I feel the SC3 32mm might be the total equivalent of the KDX220R PWK33 airflow area, as unless the 32mm version measures smaller than 32mm round (+ the extra cutout at the bottom that is more narrow adding more cross-sectional area).

I have a prototype SC2 36 body they sent me for KDX test fitment 2 years ago, which did not fit at all.
I'll have to measure it's i.d. and see if it's an actual 36mm + the extra cutout at the bottom that nakes their venturi bore an upside down egg shape, or if the 36mm is just the equivalent of a 36mm round venturi with the lower criss sectional area added to the remainder.

I'm sure with the 220SR head + cylinder being factory matched to an old fashioned round slide 28mm, the SmartCarb SC3 32mm would still do quite well on my proposed setup, although there may be almost no compromise in stepping up to the 34mm version of the same body for long term flexibility if I choose to run more of an RB'd head profile with it to support more upper RPM power.

Just a thought on the keihin 28mm, you would need the matching carb boot and and plastic reed Insert, then you will need the smaller air boot to the airbox and ideally the smaller snorkel, all standard on the SR model , without these you will lose airspeed/venturi
My keihin pe28 is the Thai version that came out on the nsr150 so it's slightly different than the original Japanese version, it has holes in the emulsion tube and a replaceable needle jet, I think it's a copy version but here in Thailand parts are so cheap for it I can't go past using it, a new slide and needle is 7 dollars as an example of cost, needles are available from Japan through webike, also have the option of original honda nsr150 needle that costs just 3 dollars but that needle is too rich on the straight diameter
I think I will have to look at making a custom needle jet, stock is 2.60mm inside diameter but that is too rich for Thailand close to the equator, long term I'm hoping to get it dialed in, get the lectron dialed in in the other bike and do a back to back shootout on tight single track, Is a thousand dollars lectron really much better than a 50 dollar keihin pe28, thought that would make for a very interesting YouTube video

kdxdazz wrote: 07:03 pm Oct 14 2025 Just a thought on the keihin 28mm, you would need the matching carb boot and and plastic reed Insert, then you will need the smaller air boot to the airbox and ideally the smaller snorkel, all standard on the SR model , without these you will lose airspeed/venturi

Interesting thoughts there, kdxdazz. The airbox boot and inlet manifold would work well for a PWK28 carb or the Lectron Billetron mini as well, or the SmartCarb SC3 28mm or 30mm versions... I'd figured one would have to machine some adapters to fit them! I won't be trying this route though personally.

kdxdazz wrote: 07:03 pm Oct 14 2025 My keihin pe28...
I think I will have to look at making a custom needle jet, stock is 2.60mm inside diameter but that is too rich for Thailand close to the equator,
long term I'm hoping to get it dialed in, get the lectron dialed in in the other bike and do a back to back shootout on tight single track, Is a thousand dollars lectron really much better than a 50 dollar keihin pe28, thought that would make for a very interesting YouTube video

I don't believe I'd spend any money or any significant time on attempting to extract maximum performance out of a 1960's/1970's technology round slide carb like the PE28, & instead, I'd be looking at a PWK28 from the SuperMini motocross bikes or better yet from a trials bike application if you can find a deal (the needle might be more appropriate for the KDX220SR cylinder head squish band profile there from a trials bike application PWK28).
I several 4-cylinder racks of sought after high performance Keihin CR31 round slide smoothbore carbs ($1000 new), and 1 rack of the equivalent Mikuni VM29SS smoothbore carbs for my '77-'79 Suzuki GS street bikes, & at this stage of understanding performance engine tuning, fuel atomization and jet signal etc, I'm contemplating selling them all in favor of dropping big money on Mikuni RS34 flatslide carbs with accelerator pumps due to their superior jet signal and fuel atomization leading to better performance.


Surely a 28mm OEM take off carb vs a $749 Lectron Billetron Pro Series or $649 Smart Carb SC3 34mm shootout would make a great read, but due to the technological advancements from round slide basic old school carbs to the flatslide technology, it'd only be a novel read with minimal interest for most. A PWK28 vs those high dollar carbs, however, on a 220SR, would be a very immersive read in terms of a budget low speed technical trails carb alternative.
After the Lectron Billetron Pro Series carb came out, the first guy I talked to at Lectron was adamant about me experimenting with the Billetron mini on my 220R, statng that he'd dome the same on a KTM 250 XC-W with incredible results for low speed technical terrain... He insisted the Billetron Pro Series would not fit the KDX whatsoever. Well, I talked to an inside connection at Lectron, and got a scrapped Billetron Pro Series carb body to test, and with the manifold spigot diameter turned down to KDX PWK diameter in the lathe, and the airbox bell long body adapter extension turned down closer to the KDX airbox boot diameter, the Billetron Pro Series fits the KDX220/200H far better than their listed Lectron Legacy Power Jet carb fitment does, so I went that route and am very glad I did.

Adapting a PWK28 on a budget would be my direction for the 220SR if I were you, dazz... You're investing in old school technology (round slide) when you could have a modern more advanced proven superior carb design in place investing similar labor hours into with greater successes in the end. I hope that sits well with you. I know the PE28 carbs are plentiful there, but I'd want to strive for the best possible setup.

You know, I had asked them for some very basic dimensions in the past so I could 3D print and test the fit, but they weren't interested in giving me the info......... kind of burns me I gotta pay for the 3D model when it costs them nothing, but it what it is......... let me know if and when you test fit one Chuck! I won't get to printing and fitting one until likely December sometime.

You may be right on the flat slide PWK 28 being the better option, I'm just so impressed with round slide.carb I have, the way it responds to air screw mixture adjustments, I also have a copy pwk30 sitting on the shelf, I could connect that up to compare to the round slide and connect the wideband to check the AFR is dialed in. Anything genuine keihin is not really an option here in Thailand unless it comes from the older honda nsr150 and Kawasaki kr150

On a different note I did contact Matt denecke about 2 years ago to tell him the problems of dialing in a lectron close to the equator, he told.me that building up the needle with a thin layer of fuel proof epoxy can be done so that's what I will try in combination with the wideband sensor, I didn't have the wideband sensor last time I tried setting up the lectron so I'm much better prepared. I have a fuel resistant 3M product that can be thinned down with acetone to give a very fine layer on the metering rod

Kawibunga wrote: 09:06 am Oct 15 2025 You know, I had asked them for some very basic dimensions in the past so I could 3D print and test the fit, but they weren't interested in giving me the info......... kind of burns me I gotta pay for the 3D model when it costs them nothing, but it what it is......... let me know if and when you test fit one Chuck! I won't get to printing and fitting one until likely December sometime.

This 3D printed model that you can buy from them for $20 per carburetor is a new thing which I have never seen. They also offer the 3D print file download for free if you want to print it yourself, which I believe you may have been referencing.

I'm pretty certain these will fit our bikes especially since they are similar to the Billetron and that they are a short body carburetor requiring a long body adapter, an extension on the airbox side, to span the gap. This also means that you can very likely have zero problem fitting the Boyesen RAD Valve intake or Moto Tassinari VForce4 reed block assembly, since both of those take up additional space over the OEM reed cage. The Boyesen RAD Valve with the SmartCarb SC3 34mm and an RB'd 220 head or KDX220SR head would make a great combination for low end torque if the SC3 34 will accommodate the extra thickness of the RAD Valve pushing the carburetor back several millimeters.

I believe one of the big design pushes for this size in particular was specifically for the KDX fitment which they were completely missing on their previous SC2 36 model. They had told me in the past that they would get one to two requests per week from KDX owners who would be disappointed in finding that they cannot fit the SC2 36 or any of the other available options back then to their bike.

The only issue I have is that something like just changing a pipe from a Pro Circuit Platinum 2 to an FMF Gnarly Woods will very likely require a different metering rod. Metering rods are not cheap like $16 OEM Keihin jet needles or Keihin jets. If one has the time to swap metering rods and wait for them in the mail and test, these carbs are absolutely going to be the best setup.
Perhaps one could negotiate to buy several different metering rods at a discounted price from SmartCarb in order to test them out for best tune.
As my friend found with his billetron Pro Series however, after having it dialed in on a Dyno and running it for a couple of seasons, not touching any settings, after doing a top end and gaining a lot of compression, the carburetor ran horribly! Luckily on the billetron pro series, you have full adjustment of the throttle range split into 3 different adjustments. But as Smart Carb will tell you, this is due to imprecise metering rod selection, relying on inferior jetted fuel delivery as a supplement on the low end and top end to find tune, which also adds airflow disruption from the jet tubes protruding into the venturi, disrupting the laminar airflow qualities... So a perfectly tuned Smart Carb on a setup that is not going to be changed is the best setup overall but takes potentially a lot more work to get dialed in to be absolute precision fuel delivery meeting the requirements of the engine, versus the Billetron Pro Series we'll call the number two best overall, but number one easiest to set up.

Thanks for the heads up Chuck78! I didn't read close enough and thought you had to pay for the file itself. Already download the files the checking them out. I thought they were charging for the files, nice to see I was wrong!

Kawibunga wrote: 02:53 pm Oct 15 2025 Thanks for the heads up Chuck78! I didn't read close enough and thought you had to pay for the file itself. Already download the files the checking them out. I thought they were charging for the files, nice to see I was wrong!

In more assuring news, I was just digging through a messages with a semi-local guy here who has many industry connections, searching for our convo on local suspension tuners (Corey @ ProTune Suspension & Levi @ Bonzi Suspension), & stumbled onto our June chats on SmartCarbs:



"He (Cory@ SmartCarb) claimed that the 34mm will be a perfect fit (SC3 34mm on the KDX200H)!"



They recognize how many water cooled KDX200/220 bikes are STILL in service out on the trails, due to their frequent weekly+ requests for SmartCarb offerings from KDX200/220 owners / potential customers...
If they can nail the metering rod tune for the 200 & the 220 with the aftermarket pipes, I think they'll really reduce Lectron's Billetron Pro Series sales to the KDX community, but the SmartCarb tuneability added labir efforts will also deter some, who will ultimately bad-mouth the carbs simply because they did not want to take the time to play with different metering rods to achieve the ideal tune... Other than that factor, these really I feel are the ultimate carbs for woods riding.
I'm not selling my Lectron Billetron Pro Series nor my 36mm RB'd PWK35 Air Striker Quad Vent, however! All are excellent carb choices!