new SmartCarb SC3 34mm advanced metering rod carb option

[SpruceItUp]

I got a response:

"Hi Ben,

Fitment was more of a challenge in the H series bikes than it was the E series, but even so our prior closest size, the 36mm, had spigots much larger than those of the stock Keihin PWK35.

In our new 34mm SC3 we have perfect fitment and clearance for both frame styles.

Shall we send over an invoice?

Happy to answer any additional questions you may have."

Looks like I'm buying another carburetor! haha

[Chuck78]

I came here to post the same news! My friend James who is a member here also got this email as well as some others in some other KDX communities.

I believe that's $50 off the regular price, so now is a good time to jump on it.

[Chuck78]

Although I had read the email from another forum member's (jz05220r?)!screenshot that he sent me, I just now dug through all the spam and promotional emails and read and replied to mine from yesterday.

Of course as you might expect from me, I sent them a long email about tuning parameters and exactly how the bike was spec'd out that they Dyno tested these on, and asking if they dynoed a 220 model specifically, and if it had a modified head, aftermarket reeds, etc....

I advise them that they will see a large amount of 220 customers that probably already have a Ron Black modified rechambered & milled 220R head or a Jeff Fredette milled 220R head, both of which will run a much tighter squish clearance than stock at around 1.0 mm, with the Jeff Fredette heads requiring a bit higher octane, & the RB had running happily on 90 or 91 octane.

I'll see what they have to say. I offered up Port timing specifications as well if they wanted to know much about the 200 versus 220 if they had not dug in that deep, but I think the info with the heads that I gave them and also questioning about aftermarket reed assemblies is probably the extent of what needs to be discussed outside of supporting modifications done to a select few cylinders.

Usually the RAD Valve and the VForce 3 generally require stepping down one size in pilot jet. I failed to mention that detail to them, although I think the effect will be similar to that of the patented CloudForge Venturi design of the smart carb, so maybe it will not change the air velocity any further than the carburetor itself changes it, although it could enhance the air flow velocity even more by going with the aftermarket reed cages.

[SpruceItUp]

Nice! It'll be really neat to try this out on the KDX. Hopefully I'll have more luck with it than I have had with my Lectron. It seems like it'll be even easier to tune than the Lectron is, anyways.
I chatted on the phone with Kim at SmartCarb yesterday when I bought it, went through modifications to my bike etc. Just the usual suspects on my 92 in terms of modifications.

This has me wanting to finally get off my butt and go tinker with the KDX again. Can't wait.

[Chuck78]

After replying to the customer requests list mass emails that SmartCarb sent out as quoted above, as well as SmartCarb staff doing a pretty exhausting amount of research on various KDX175-200-220 iterations and variants and fitment concerns, I had the pleasure of receiving an unexpected phone call from a Mr. Nathan Dyess of SmartCarb as I was putting away dinner leftovers tonight...

We chatted for a good long while about different KDX 200 and associated variations as far back as the KDX175 & KDX200A, and the 220 of course...

Corey, the main engineer and I believe one of the two founders of SmartCarb is going to get back with me tomorrow on the more technical details that Nathan needed to refer to him for, but to say the very least, I'm incredibly excited about this carburetor.

From talking with Nathan, it sounds as if their long-standing development of this internal venting design is much better at reading and delivering what the engine is requesting/requiring in terms of fuel delivery versus externally vented versions of metering rod carburetors, so much so, that aftermarket reed cages, which on a Keihin PWK35 would generally require stepping down to one size smaller pilot jet, as well as pipe swaps to a different tune configuration of expansion chamber, don't necessarily need a metering rod change.

The one thing he did state however was that milling the head for higher compression is definitely more likely to require a metering rod change as that is a pretty massive variable to alter in terms of the internal ventings ability to compensate.
He also mentioned tightening up the squish band could potentially need this as well although I'm pretty certain that just milling the head for tighter squish also resulting in a much higher compression ratio will be much more so inclined to require drastic changes of swapping out a different metering rod, vs the Ron Black / RB Designs 220 head mod which is a completely re-chambered had to return the compression ratio to basically stock or slightly higher so that the bike is quite happy running 90 octane in any weather or trail conditions. Hopefully Corey can shed a little more light on that aspect in particular.


To summarize a long story that is likely on the Smart Carb website, which Nathan and I also discussed as he reminded me of what I had forgotten.... Corey had been going in depth developing this internal vented metering rod carburetor technology since the early 2000s in the two-stroke engine world specifically for a grant-funded project to make cleaner burning two-stroke snowmobiles. They had actually bought up all of the patents from the originator of the Lectron metering rod carburetors, the guy who sold the Lectron company early on because he wanted to pursue this internal venting design (which wasn't what the majority of the decision makers at Lectron wanted at that time), as he knew it was the end goal and the future. Since then, they have been working diligently for the past couple decades now perfecting this technology that you see almost the end result in with the previous generation SC2 36mm. The SC3 utilizes basically the same technology but is a more refined version which also is easier to manufacture while not having any downfalls that would make the more complex production and design of the previous generation more expensive.

I'm pretty psyched to try this out, so I've got to expedite my top end tear down to sometime next week so that I can be ready to try one of these out here within the next 5 weeks... There's a bit of a lead time on these so that buys me a little bit of time while I get hard at work try to finish up this house renovation along with some hired help from two guys from our riding crew who are eager to assist both for some monetary kickbacks as well as finally freeing me up so that I won't decline any further trail ride weekends!


They've been dyno tuning and testing on a 200H, and have been field testing a 220 as well based off of the dyno results of the 200H.

They felt pretty confident about about metering rods specification, and Nathan had told me that the vast majority of all of their applications use basically a small range of metering rod that spans only five different profiles for I'm going to say something like 85% of their applications, maybe even more, that's just me guessing.



This is a pretty great development now and cheaper than the Billetron, although I do really like the Billetron Pro Series with the latest generation metering rods they have developed... I think the Billetron sales will definitely drop off for the KDX with the price point alone of the other high-end metering rod carburetor on the market for our bikes, the SmartCarb SC3 34mm...

When reaching out to both these companies a few years ago inquiring about KDX fitment, Smart Carb were very eager and enthusiastic to talk to me and even sent me a carburetor body to test fit and machine in any way imaginable that would be reasonable modifications to fit our bikes. The end result was that it did not fit without frame modification. Fast forward a few years and here we are, they have developed this new version that does fit!

Lectron we're not so great to work with initially because they were pretty old school. They actually wanted me to buy and run for full price a billetron mini design for the super mini KX100 type bikes. The guy pushing this said that the billetron would absolutely not fit the kdx, but I knew from the spec sheets and measurements that it actually would fit pretty nicely... The only way I got electron to actually work with me on this was reaching out to their former lead fuel systems engineer outside of his workplace, Matt Denecke, currently of his own company Denecke Racing Technologies... He was really stoked to discuss these options with me, and that was really the only way that we were going to get a listed KDX fitment for the Lectron Billetron Pro Series carbs.... Sidestepping the traditional customer service contact routes and taking matters into our own hands!


Long story short, smart carb was incredibly eager to work with the KDX community on making a fitment based on the amount of requests they continually received about KDX fitment, but Lectron was not so easy to deal with until I contacted the right person at Lectron who the general public would not normally be able to reach through any business channels....

I think these are both awesome carburetors, but I really feel that due to the price point and their eagerness (in both customer service as well as research and development breakthroughs and continual refinements), as well as their domination in the enduro market, the SmartCarb is going to really sell well.

A genuine Keihin PWK 35 Air Striker now costs $425-$450!!!
I'd proven years ago riding the old school powerjet Lectron on my then fresh 220 with an RB modified head, that metering rod carbs were the way to go, as I got excellent throttle response out of that 34mm Lectron, real good power, and significantly better fuel economy than anyone else in our riding crew, who basically all ran PWK carbs on KDXs, KTM 200/250 & a 300, Honda CR125R & CR250R, etc... returning back to camp or to the trailhead, there was never a time where I did not have significantly more fuel left in my tank versus anyone& everyone else... And I was generally riding faster than and farther ahead from everyone, which would burn more fuel typically, as well as doubling back when I'd stop for them to catch up and they would never show up, turning around and helping them on the tricky hill climb spots and other bike recoveries from lay downs.... So more trail mileage than anyone else as well as a more heavy throttle hand, yes still significantly less fuel used.

I have really grown to appreciate the fuel efficiency from the metering rod carbs as well as small turbo diesel engines in my 4-wheeled transportation... VW 1.9L & 2.0L turbo diesel swaps into smaller 4WD pickups etc is another passionate niche interest of mine, to say the very least.