Lectron 38 HV Carburetor

I recently got my hands on a new 2018 KTM 150 SX, and I'm really getting a feel for the bike. I’ve actually spent quite a bit of time riding it in completely stock form, and if you follow my YouTube videos you’ve likely seen that the bike had some sputter and bog at roll-on with the stock Mikuni TMX carb. Yeah, I've dabbled with the jets that came with the bike, as well as tweaking the needle position, but never really got it running the way I'd envisioned. It actually made the bike a bit frustrating to ride, and the power was disappointing. That's why I made a call to Lectron in hopes of remedying the frustration I was having with my new orange two-stroke. Yes, I could have dedicated hours and days at the track, fine-tuning the TMX carb to possibly run better in specific environments, but I'd much rather be riding than tinkering with the carb. Lectron said they could solve the issues I was experiencing with their 38mm High Velocity Carb and installation kit. That meant it came with the carb ($415), XCW Airboot ($60 for the '17/'18 KTM), Domino throttle assembly ($39), and a slightly longer throttle cable ($35). That's a total of $549.

First Impressions

I've had quite a bit of experience messing around with different carburetors over the years, including a Lectron carb on my old 2002 CR250 project bike. Everyone has their own preference when it comes to carbs and how to get the various jetting circuits working their best, but with all the research and testing I’ve done over the years, I really appreciate the technology that Lectron has, and understand why it works. Their product is very high quality, which is obvious as soon you take it out of the box. Something cool and unique in comparison to most carbs is that the float bowl area is made of hardened clear plastic. From the exterior you’ll notice a few minor differences in the appearance compared to a traditional Keihen or Mikuni, but what you’ll find on the inside is where the magic lies. The patented metering rod is what defined the Lectron and how it helps create a unified fuel circuit that's unlike a traditional carb. Leveraging a mechanical venturi effect between air and fuel, the metering rod helps provide the most efficient delivery of pre-mix to the engine over a wider range of conditions, ie: altitude, humidity, weather, and fuel mixture. The entire kit came together in one box, and was accompanied by the necessary installation instructions.

Since I’ve dabbled with plenty of carbs and two-strokes over the years, I actually left the instructions on the workbench (usually a bad move), and started tearing down the bike. Since I’m definitely not familiar with the new KTM plastics and subframe, it took me awhile longer than it would have on a Japanese model bike to get the rear removed and the subframe pivoted up for easier access to the air boot. The air boot swap was required for the Lectron fitment, since the spacing is slightly different than the stock SX spacing. Once the airboot was replaced, I was able to easily remove the stock Mikuni carb and swap it out with the Lectron unit. You'll want to install the intake boot side first and then drop the subframe back into place and seat the airboot side onto the carb. I definitely had to finesse the carb a bit on the intake side since it sits a ways further into the boot than you might initially expect. Once the carb and subframe were back on, I removed the fuel tank and just traced the throttle cable path with the new assembly to match the stock routing to the carb. All in all, the installation took about an hour-and-a-half with no directions used. I would imagine being able to do this again in less than an hour if I kept up a good pace. The carb itself is very easy to swap, and if you plan on back-to-back testing, I wouldn’t imagine it taking longer than 10-15 minutes if your bike doesn’t require an air boot swap.  

On the Track

It may be helpful to reference the included video for this, but the first startup went very well.  After three kicks the bike fired right up, and I let her warm up. The carb doesn’t like to start cold without the choke on, and I’ve learned that even if it’s warm out, turning the choke on upon first start of the day is essential. After letting the bike warm up, it was instantly noticeable that the snap upon roll-on was drastically improved...even while sitting on the stand in the garage. I also quickly realized that while the roll-on snap was improved, it still had a very slight hesitation. Being that I’m at about 3,000 ft elevation here in Boise, Idaho, I decided to lean out the metering rod just a quarter turn as suggested to make that initial throttle hit more crisp. It took me about two minutes to pop off the top of the carb, and with the metering rod adjustment tool Lectron provided, I was able to make the adjustment and start the bike again. Now it was in almost perfect running condition.  

Once I got the bike out on the track, I was absolutely blown away at how much more power was on tap in all areas of the powerband. I had much more initial roll-on power, which was transitioning in one smooth increase from bottom to a much-improved mid hit, and it continued through a broadened overrev. The stock Mikuni may not have been jetted to its full potential, but in retrospect, the Lectron is a bolt-on mod that instantly transformed my 150 SX into the bike I was hoping it would be! 

One thing I'd like to change on the Lectron is the location of the choke. It's currently set up on the right side of the carb, which means I have to reach across and over the carb to turn it on for first kick. Not ideal, but given that I only have to do this once per ride, I won’t let it get to me too much. Since installing the Lectron, I have about ten rides on everything from tighter fairground-style tracks, to open motocross layout tracks and even some higher elevation 4,500 ft+ trail rides, and in ALL these conditions the bike has remained consistent and strong. I have not made any additional tweaks or adjustments to the metering rod or idle since installation, and have been more than satisfied with its continued performance.  

Long-Term Durability 

I haven’t experienced any signs of wear or malfunction with any of the units provided by Lectron and wouldn’t expect to anytime soon!  The carb cleans up easily, and the throttle assembly has also worked just as designed. 

Last Words

If you have a two-stroke, and like me, you don’t enjoy constantly playing with jetting, then I'd suggest that you quit reading this review and head over to Lectron’s website to order the applicable carb for your bike.  Whether you have a new 2018 two-stroke or a classic Elsinore, I'd feel confident in saying that you won’t regret spending the $500 or so for this bolt-on gem!  I’ve played with and tested many products over the years, and I would have no hesitation in placing this product in my top three for best bolt-on mods! 

Vital MX Rating: 5 Stars - Spectacular

For more info and all the available options, head over to LectronFuelSystems.com.

About the Test Rider

Shelby Paget - is a ginger that has been rockin' two wheels since he was three years old. Growing up riding singletrack and trails in the hills of NorCal with his brother and Dad until he got his first taste of the Motocross Racing scene at 14. He's been hooked ever since! Whether he's working on looking better than he really is for the camera or doing cartwheels down the straights, he's always looking forward to getting back on two wheels whenever he gets the chance. This 5'11", 150 pound ginger will be riding as long as he has a wrist to twist!