SmartCarb® vs Lectron®
SmartCarb® vs Lectron®
How do they compare?
We get this question a lot. Both the SmartCarb® carburetor (SmartCarb®) and the Lectron® carburetor use metering rods in lieu of jets and needles, and both manufacturers make similar claims in terms of performance, air density compensation, and ease of use. Understanding how they compare is the first step to making an informed decision on which one is right for you. In this article we’ll cover a bit of the history of both products and then provide an objective comparison.
Disclosure: Lectron® is a registered trademark of Lectron, LLC and is used herein without permission. Lectron, LLC and Lectron® carburetors are not, and have never been, affiliated with SmartCarb Fuel Systems, Inc or the SmartCarb® brand of products.
Same original inventor, same concept, same thing… right?
Nope! While both carbs use a metering rod and a flat slide to provide precise air/fuel mixture control and superior fuel atomization to that of conventional needle and jet carburetors, there are more differences between the two than are readily apparent.
Always looking to do things better, Red, and more recently SmartCarb Fuel Systems, have evolved the metering rod carburetor concept over time by adding improvements and features to enhance the basic operating principles of the technology while also addressing the shortfalls and limitations of prior designs. The result is a fuel system that is substantially different from its predecessors, including the Lectron® carburetor.
Like most conventional carburetors, the Lectron® carburetor uses a circular venturi shape. The SmartCarb® does not. Instead, it uses a patented “inverted egg” or “keyhole” venturi shape. The thinking here is not unlike what backyard mechanics have been doing for years by oval/offset boring conventional carburetors – that is to change the rate of throttle opening through the throttle range. SmartCarb Fuel Systems takes it further by algorithmically determining optimum venturi shape, size, and throttle rate for various applications, taking into account a number of engine-related variables.
There’s more to it when it comes to metering rod carbs like the SmartCarb® and the Lectron® carburetors. Maintaining sufficient air velocity or “signal” at the rod is critically important for fuel pickup and atomization. Any stalling of velocity or weak signal at the metering rod can result in a loss of fuel pickup and poor atomization, translating into hesitation, bogging, or soft throttle response. The SmartCarb® carburetor’s venturi profile is designed to focus airflow directly at the metering rod through the entire throttle range in order to maximize signal and promote fuel atomization. A circular venturi shape is not optimized for this purpose and as a result is more prone to suffer from weak signal and soft throttle response, particularly down low or just off idle.
Float Bowl Venting
Float bowl style carburetors require float bowl venting to work properly – just ask anyone who has ever had plugged or frozen vent lines. The Lectron® carburetor, like more conventional carbs, vents its float bowl through external vent/overflow hoses that hang down in front of the rear wheel. The SmartCarb® vents its float bowl quite differently – from inside the airbox via a scoop/port located in the top of the venturi bell.
This patented internal venting feature allows the SmartCarb® to compensate for a wider range of air densities compared to other carburetors. Recent testing proves air/fuel mixture consistency up to a simulated 22,000 feet on drone engine applications, for example.
Venting and airflow communication between the airbox and the float bowl applies a steady, equalized pressure against the fuel in the bowl that is proportional to air density and also velocity inside of the airbox. Put simply, more dense, heavier air drives more fuel flow, less dense air drives less fuel flow, and air/fuel ratios stay consistent regardless of elevation or temperature changes.
Beyond improved air density compensation, internal float bowl venting also provides for sufficient top end fueling in the SmartCarb® without the need for a power jet. Although the original Lectron® carburetor of 1974 did not have a power jet, all modern iterations of the design come with at least one or more power jets to provide additional fuel to the mix from mid to top.
No overflow hoses?
Where does the fuel go in the SmartCarb?
Unless you count the Lectron® carburetor’s power jet as a jet (and it is), both it and the SmartCarb® are jet-less in the traditional sense. That means no more brass to change either way! Adjustments are typically required during initial tuning and to accommodate engine modifications or when changing fuel selection.
The Lectron® carburetor has 3 primary adjustments: the idle set screw, the metering rod position, and the power jet. The SmartCarb® has only two: the idle set screw and metering rod position. Changing the metering rod position in the Lectron® carburetor requires removing the cap and pulling the slide. Lectron® carburetor metering rod adjustments are limited to 4 positions per revolution.
Conversely, changing the position of the metering rod in the SmartCarb® is done externally, by hand, and from the seat of the bike in most cases. The SmartCarb® carburetor’s metering rod can be more finely adjusted with 10 clicks/positions per revolution by shutting the engine off, opening the throttle to wide open, and using the clicker adjuster in the cap. Adjustments take seconds and can be done while the engine and pipe stay up to temp.
The SC2 model SmartCarb® and H-Series Lectron® carburetors are designed for use in modern 2-stroke dirt bikes and similar applications using the Keihin PWK or Mikuni TMX stock, however their build quality and manner of construction differ in a few notable ways that affect their appearance, compatibility, durability, and ease of use.
The cast aluminum H-Series Lectron® carburetor, based on a much older design, presents a few issues when used in modern applications including:
- Longer end-to-end length (.5″/12.5mm longer than the modern Keihin PWK/Mikuni TMX and .25″/6mm longer than the SC2)
- Stock throttle cable incompatibility
- Inconvenient, pipe side choke placement
- No throttle position sensor (TPS) option
- Significant throttle slide wearing over time (replacement required)
All of this means the fit in some bikes can be tricky (for example, Lectron, LLC recommends the use of the shorter XC-W or TE intake flange with the HV or H-Series models when installed into 2017 or later KTMs or Huskies). The stock throttle cable and handset must be replaced with ones provided by Lectron, LLC in most applications and the use of 3D ignition mapping, Beta oil injection, or aftermarket CDIs requiring TPS isn’t an option.
Which one is right for you?
The choice is ultimately up to you. Our hope is that this article sheds some light on the history of these revolutionary fuel systems and that it offers a clear and concise explanation about their differences. Knowledge is power and an informed decision is a smart decision.
Stay tuned for a comparison video coming soon to our new YouTube Channel!
thank you for the information
will i need to make airbox mods on my 2020 65 ktm to get the carb to fit
I have a 2022 KTM 125xc, interested in either the SC2 or the new Billetron 38, but unsure of the major differences between the 2 other than the cost of them. Can you point me to an area where I can read or see the differences?
Hi Wesley, thank you for your interest in the SmartCarb. The differences between the SmartCarb and the Lectron as explained in this article still hold true with the Billetron, with the exception of better fitment. The Billetron now fits as well as the SC2, but functionally it is the same as the earlier H Series model. The Billetron is still 4mm smaller at 34mm in size, is not externally adjustable like the SmartCarb, and is not internally vented like the SmartCarb. We recommend the 36mm size SC2 model for your 125 XC and you can view it here: https://technologyelevated.mysites.io.flywheelstaging.com/product/36mm-sc2-smartcarb/
Let us know if you have any further questions.
Hellow, i have now the h serie lectron on my husqvarna te300 2017 and it runs great, just the choke en throtle cable on the lectron is a mess.
Is the smartcarb better then the lectron?
Hello Sebastian, thank you for your comment. We encourage you to read this article comparing the SC2 SmartCarb to the Lectron H Series and determine that for yourself. Apart from the fitment issues you mention, the SC2 SmartCarb offers a few features and benefits that the Lectron carb does not including full external adjustability with much finer adjustment resolution, integrated, internal float bowl venting, and variable throttle rate venturi shape. We believe the SmartCarb would be a definite improvement over your current setup on your TE300. We recommend the 36mm size SC2 model, on sale now through 12/4 here: https://technologyelevated.mysites.io.flywheelstaging.com/product/36mm-sc2-smartcarb/
Greetings from Canada
I have an 06 cr125r
It’s been ported. VForce3 reeds, Pro Circuit Platinum Pipe with Shorty Exhaust. All top end, very week bottom. 32:1 with 91 octane pump gas.
Having lots of issues, mainly plug fouling and very temperamental jetting.
I’ve been trying to decide between a PWK airstriker, Lectron, & smartCarb for a while.
I’d like to be able to ride slow while still being able to ride wide open at tracks. Do you have any suggestions?
Hi Gio, thank you for your interest in the SmartCarb.
The higher revving 125s are typically a bit trickier to get dialed. They come with a 38mm size carb stock, but we recommend our 36mm size instead. It will give you gains bottom to top and also make the tuning a bit easier being slightly smaller. The SmartCarb’s venturi shape is designed to give you what you’re looking for: crisp and clean bottom end throttle response with a linear transition through the mid to the full bore on top. The other two carbs are solid fuel systems, but they don’t do what the SmartCarb does for your performance and ease of use.
Here’s a link (no TPS required): https://technologyelevated.mysites.io.flywheelstaging.com/product/36mm-sc2-smartcarb/ We’ll pre-tune it specifically for your setup.
Hi, do you recommend a pair of carbs that would work on a CCM with the 710cc, twin carb version of a DR650 engine, running around 70bhp with cam and headwork, would need 1 TPS sensor for ignition
Hi I’ve got a 1990 rmx 250 do yous do anything for them thanks
Hello! Is the SmartCarb can be installed on older bikes?
I have 2 stroke Kawasaki KDX250SR 1991. I’m going to use it with snowbike conversion at winter, as well as dirtbike at summer.
What carb do I order for my yz250f 2004 it is a 4 stroke and I’ve been having carb problems since I got the bike I’ve went threw two keihens and I’m over the hole rebuilding and jetting process I live in Florida I only ride in the southern states and I’m mainly on the track but I do alot more freestyle then I do racing
Just curious what you guys recommend for my 98 cr 250?
I strickly use the bike for motocross.
For a pure MX CR250 we recommend the 38mm size SC2 with No TPS. View/order here: https://technologyelevated.com/product/38mm-sc2-smartcarb/
would this fit on my 2001 kx250? i know that the lectron wont work because it doesnt have a throttle position sensor.
Hi Porter, thank you for asking. Yes we recommend the 38mm size SC2 model SmartCarb with Standard TPS for your 2001 KX250. View/order it here: https://technologyelevated.com/product/38mm-sc2-smartcarb/
The TPS will allow you to keep the 3D ignition mapping feature in your bike. We’ll pre-tune the carb just for you taking into account engine mods, riding style, and fuel selection/oil ratio mixed. You can also consider the smaller 36mm size SC2 with Standard TPS if you’re primarily looking for bottom end torque/response/fuel economy.
Hi guy’s, do you have set’s of 4 smart carb’s for a 1992 cbr1000f motor? As i am creating a monster and i would love to try your wonderful product, i know it’s an old bike but so am i and if it’s possible it would be plenty fast for me. ?
Hello my name is Robert, I live here Japan. I was thinking of purchasing a Lectron but you’re got my full attention. I have a ‘99 MBk Stunt(Yamaha Slider)vertical Minarelli, 2 stroke mods are: Most 70cc high end bore kit, Most racing exhaust, custom intake with V-Force 8reed, Pwk 28 carb (slow jet 48, main jet 145) . Spark plug is NGK BR9ECM the same that is used on NSR250 and no air box only velocity stack. Well nothing is stock anymore, it doesn’t even look like a Stunt, I do mostly street racing and either the throttle is closed or fully open. I use 100 octane pump fuel pre mix at 50 to 1 oil ratio, . What do you recommend and is it available? By the way, my sister live really close to you, your located in Raytow she lives in KC about 20 minutes from the KCI Airport. Thank you for your time, Robert Sasagawa
I hear one of your customers are testing a 38 mm on a BMW R100 RS with good results and I read the Ducati 900 article. Would you consider making asymmetric sets for BMW airheads and if so when might that be .. ?
Hi Niels, yes we’ve equipped around 5 R100s so far with great results. Asymmetrical or mirrored versions are coming but not likely until toward the end of the year.
Wonderful, I won’t be riding until March 15 anyway. Can you spill something about what “great results” means, dyno hp, economy and emissions? if you can post something on your site when ready, then I can make propanda for them maybe .. question: in the Smartcarb vs Lectron article your metering rod is shown, but I would like to see how the holes are made on it .. and what is the blue hose going from the bottom doing?
Sorry I overlooked the manuals says the blue hose at the bottom is just a drain. Is the BAC model, which subjectively looks better to me, also sold or just the ones that show on the Shop page? Are you planning asymmetric/mirrored versions for other two cylinder older bikes?
Hi!, I have a Banshee with 2-into-1 intake system (one carb for both cylinders). What do you recommend, 36mm or 38mm?
Hi Jose, we recommend the 36mm for a mostly stock Banshee with 2-into-1 intake. Are you using 1 or 2 pipes?
Hello looking to buy a 2015 yz85 FOR my son and would love info on WHEN you WILL have the carb BACK in stock
Hi Dan, we’re planning on having the 28mm size SC2 SmartCarb available in the coming few weeks. Send us an email at email@example.com and we’ll add you to our list to notify of availability ahead of a general announcement.
What setting should I start with i have a smart carb 38 ca kn air filter and open air box v force 3 reeds?
Also its a Honda TRX250R 2 stroke.
Hi Lloyd, for a 38mm Cast model SmartCarb we would recommend the A-Q07 metering rod at around 45-50 clicks from full rich. Depending on engine mods and fuel selection, the step richer A-Q05 may be recommended. Any engine mods on this TRX250R? What fuel type and oil ratio are you mixing?
Tengo una yamaha dt200wr q me recomiendas de cuantos mm me recomienda el carburador SmartCarb SC2
Ok im currently Racing 45 flatheads and running Lectron.what do you have and Price! And any Sponsorship !
sir my motorcycle is 1999y cagiva mito 2 stroke street bike
can i use smartcarb on my bike?
it is for only premix dirt bike?
Hi, I have a 2010 Raptor, I was upgrading to a Mikuni TMX 35 set up with a full arrow system and V force 3. I bought the TMX New and jetted it. I hated the Mikuni set-up. I have fitted the SC2, I haven’t ridden it yet but is already running so much better. Be warned there are lots of mods needed to fit it. The new manifold that I made for the 46mm spigot of the carb, cut a small amount from the frame 3mm high and 30mm wide, cut the air pipe from the airbox back by 13 mm. The SC2 is a lot bigger physical size than the Mito carbs but it will fit. I would say it is not easy to fit but is doable if you can get a manifold made. What I can also say is that the bike seems very responsive and idles like a dream. Looking forward to some better weather to get it on the road.
Hi Team SmartCarb,
I am planing to use your carb on my PX200 251cc engine. what size of the Smart Carb which i use it?
What about 4 strokes
1 . The SC can be used for 4stroke engine?
2 . I have suzuki v100 scooter ( 2 stroke )
can the SC be used on my motorcycle? what is the right size?
Was wondering about vintage bikes, I have an 81 YZ 465 and would a smart carb fit, the stock Mikuni 97 mm long and I don’t have a lot of height before it hits the frame . I live at 6500 ft elevation but go to around 500 ft and up to 9000 ft so no jetting would be real nice. Thanks for time. Dave
Can this work on my moped .. it uses a bing Carburetor
I have `17 TC125 running the 144cc top end. It is modded by Tom Morgan. He ported and adjusted the compression. Although I dont know exactly the spec changes he made (port height changes, squish changes etc).
What info do I need to get from him, for a SmartCarb to be properly set up?
I also run: V force reeds, ProCircuit pipe and shorty silencer and 32:1 pre-mix of 50:50 mix of 92octane non-ethanol pump to 110 Trick race gas which yields about a 101 octane mix w/ Maxima Super M.
FYI – Im currently running a JD kit, but it is not perfect. I still get an occasional bog off idle, or at a steep forward angle, despite using JD`s recommended settings as well as changing things around a bit.
and….will a SmartCarb for my TC144 be able to retrofit to a differing bike in the future such as a 2020 TC250?
Hi Robert, thank you for your interest in the SmartCarb for your Tom Morgan modified 2017 TC144. It would be very helpful to us in pre-calibrating your SmartCarb if you could gather the following information from him and also provide further information yourself: difference in compression from stock and what your current, best jetting specs are with the JD kitted carb. If Tom provided jetting specs for his mods they would be helpful to know as well. We’ll take that information and use it to set your SmartCarb up accordingly. Questions from us: how do you ride this bike, or what is your riding style? How would you plan to ride the TC250?
We recommend the 36mm size SC2 model SmartCarb for your 144, available here: https://technologyelevated.com/product/36mm-sc2-smartcarb/ We typically recommend replacing size for size but there are some notable exceptions, the 2017+ KTM/Husky 125s and 150s (includes 144 kits) being some of them. Our 38mm size is just a bit large. That said, and to answer your question about the TC250, the 36mm size we recommend will work very well for either your current bike or the 250 and it is by far our most popular size. For the 250 a 36mm or a 38mm are acceptable and either will be an improvement everywhere over stock, however the 36mm will prioritize bottom end snappiness/responsiveness as well as fuel economy gains. Choosing a 38mm for a 250 is done when the top end needs prioritized as it will extend the powerband and provide an additional 500-600 useable RPMs over stock (think pure MX, snowbiking, desert racing, etc).
Feel free to reach out direct over the phone or via email at our Contact Form (https://technologyelevated.com/contact-us/) for assistance. We are happy to help!
Do you set a baseline in the carb for the applciation? for example, I have a WR250 with a Gnarly Pipe and FMF turbine core?
Hi Franky, yes we do. Every SmartCarb is set up specifically for the application for which it was ordered. We ask for the year/make/model, what notable engine and exhaust mods you’re using, how you ride the bike, and what fuel type/oil ratio you’re mixing. That information gives us everything we need to know to select a metering rod and pre-calibrate the SmartCarb just for you. Most exhaust pipes and silencers don’t affect our baselines. Mods that have a bigger effect include head modifications, upped compression, porting, bore kits, etc. We hope this answers your questions. We recommend the 36mm size SC2 SmartCarb for your WR250, available here: https://technologyelevated.com/product/36mm-sc2-smartcarb/
I have a KTM 950 with vacuum slides do you have a replacement for these carbs?
Hi Art, unfortunately we do not have replacement down draft style SmartCarbs developed yet for the KTM 950.
I run a old school honda cr125 on a shifter kart
What’s your recommendation
Its ported with rlv r4 or r5 pipe
Carbon tech reeds stock bore boost port teflon coated flat top piston
Hey James, we’d recommend our 36mm size SC2 for your CR125 shifter kart. See it here: https://technologyelevated.com/product/36mm-sc2-smartcarb/ How is your fueling set up – are you running gravity or a pump and if pump, is it a pump-around system? Also what fuel/oil ratio are you mixing at? Need to know these answers to configure the carb properly.
Do you have one that fits the YZ125 2017 model…
and is it suitable for same bore machines like a 125.
Who in the UK is the dealer for your carb
Yes we do, the 36mm size SC2 is recommended for the YZ125. Can you clarify what you mean by same bore machines? For a 125cc 2-stroke the 36mm is typically the standard recommendation, though there may be exceptions. We would need to know more about the application.
We do not currently have UK distribution, however we are working to expand our dealer network throughout Europe, including the UK, over time. You can order directly from us or you might reach out to SIP Scooter in Germany or HTM Racing in Italy for availability. They are currently our largest European dealers.
What would you recommend for a 2002 polaris edge x 700 twin snowmobile
Will you make a coolant heated option for the snowmobile market?
We don’t currently offer a coolant circulating heater, however there are two aftermarket companies that make heaters specifically for the SC2 SmartCarb. PST (Power Sports Tech) and Avid Products both make press on or clamp on heater jackets for use in snowbiking. That said we have found with our extensive experience snowmobiling that carb heating isn’t normally required as they’re completely shrouded under the hood.
Have you been addressing the street bike market with this info? Such a big market out there…
It’s a huge market and the potential for excellent results is there as you well know with your SmartCarb equipped BMW Airhead, however until we are able to better address the fitment considerations and gain a better understanding of baseline settings like we have with the off-road 2-stroke market, we’re content to let it ride so to speak for now.
I have a 2001 kx250 with a BUD racing pipe and silencer so what carb would I need?
Hi Chet, for your KX250 we’d recommend the 38mm size SC2, available here: https://technologyelevated.com/product/38mm-sc2-smartcarb/ We just need to know how you ride the bike and what fuel type/oil ratio you’re mixing in order to pre-calibrate it specific to your needs.
Thanks for your reply. My applications are Honda NSR50 and NSR80 engines with the reed block entry at 43º forward of vertical. I am currently using an adapter block that reduces this by 13º, but normal carbs are not up to the job at that angle.
The resulting 30º angle forward toward the engine is workable with a SmartCarb, however proper float level becomes just a bit more important. The stock carbs are flange-mount correct? Ours are designed to be spigot-mount with a rubber flange and clamp.
Thank you. I only use spigot mount carbs so SmartCarb is a good option.
What setting should I start with i have a smart carb 38 ca kn air filter and open air box v force 3 reeds
What is the maximum degree of downdraft that is usable with a Smartcarb?
Hi Roger, the SmartCarb in its current, vertical mount configuration, performs best being tilted no more than about 35 degrees forward and up to 15 degrees either side. We have plans to eventually release downdraft versions. What is your application?
I currently run an H series on a modified 2009YZ125 and I love it. I am considering upgrading my 2018 KTM 150sx. What smart carb do you recommend??
Hi Troy, thanks for asking. If you’re happy with the Lectron on your ’09 YZ125 then you’ll be really impressed with the SmartCarb. We recommend the 36mm size SC2 for your 2018 KTM 150SX. It’s available here: https://technologyelevated.com/product/36mm-sc2-smartcarb/ The 150SX comes stock with a 38mm Mikuni TMX and typically we recommend replacing size for size but there are exceptions, including the 150 KTMs, where we recommend otherwise. The 36mm size SC2 will increase performance everywhere compared to the Mikuni, even on the top end. You can expect very crisp, clean, and strong throttle response down low with linear power delivery through the mid to top. The SC2 is a direct fit and accepts the stock throttle cable. Let us know if you have any questions about how to order, installation, or tuning.
Thank you for a very clear comparison.
How do you pitch your carb over a Lectron user that only had problems? How do you get that person to go from $550 spent on a turd. To an $800 different version? And I mean that not as an insult. But one metering rod carb to another. I’m in that boat.
We’re sorry to hear about your Lectron troubles. That’s a tough spot to be in and we can certainly understand your apprehension to try another metering rod style carburetor after having had that experience. While we can’t help you with the Lectron you have now, we can encourage you to work with Lectron to sort out any potential metering rod mismatch or workmanship issues. You may be able to sell it also, especially if it’s one of their later HV or H-Series models. We would also encourage you to check out our Facebook Page and Instagram account for customer feedback and testimonials. The Facebook Group SmartCarb Users is also a good resource for you when considering purchasing a SmartCarb. Lastly, as we hoped to clarify in this article, the SmartCarb is more than just a different version, but rather the careful development and culmination of a lifetime’s work on this fuel system concept.
What do you ride Dario?
I know some guys that have used lectrons with some success on big bore horizontal piston imported engines Like the Daytona 190s. These engines come with a Kehin 28 mm round slide carburetor. Is there a smart carb available that might work in this application? Most everyone spending money on these motors are going up and piston size and rod length ending up somewhere between 212 and 274 cc. If there is a carburetor you offer I would expect to likely have to weld up an intake to work, but without an airbox I’m not sure if the venting would function properly, or as described in this article. We race YCF mini Flat Track Bikes, and everyone I’ve ever seen has deleted the cheap airbox and opted for a pod filter.
Yes, although it is currently out of stock, we offer a 28mm SmartCarb that will fit the stock Daytona 190 and will also work well for the stroker big bores like Pirahna, Lifan, etc. The spigot diameters are nearly identical to the 28mm Mikuni VM roundslide. A flange may be necessary for your application and can be easily fabricated, or you can make an adapter flange for the engine and use a short rubber hose with clamps for attachment.
Running a pod filter, or even no filter is not a problem. The SC will read the air density and velocity at the front of the intake bell regardless of whether a filter or airbox is used.
We will have the 28mm size SC2 SmartCarb available again in the coming weeks so stay tuned!