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PRO SERIES Carburetor Kit for 4-Stroke | Precision Fuel Delivery, Peak Performance, Ultimate Simplicity (38mm-40mm)

Name: PRO SERIES Carburetor Kit for 4-Stroke | Precision Fuel Delivery, Peak Performance, Ultimate Simplicity (38mm-40mm)
Brand: Lectron Fuel Systems
SKU: 1480-PRO
Price: 899.99 USD
Availability: InStock

Lectron Fuel Systems Throttle Cable Threaded For Thumb

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For Riders Who Want

Purpose-built for 4-stroke performance, the PRO-SERIES 4-Stroke Kit delivers instant throttle response and a broad, usable powerband — all without the need for jetting. Its billet aluminum construction, chrome-plated brass slide, and proprietary fuel system offer a smooth, torque-rich ride that adapts to changing elevation and conditions automatically.

With internal fuel routing, a precision Xcelerator metering rod, and a plug-and-play install kit (including a throttle assembly and cable), this carb is designed for riders who want simplicity, responsiveness, and maximum reliability in one system.

Includes

Kit Includes

(1) Black Anodized PRO-SERIES 4-STROKE Carburetor Setup
(1) Domino Throttle Assembly
(1) Throttle Cable
(2) Lectron stickers
(1) PRO-SERIES Tuning Guide

Built for performance. Tuned for simplicity.

The PRO SERIES 4-Stroke Carburetor delivers instant throttle response, crisp power, and easy installation — no jetting required. Designed specifically for modern 4-stroke engines, it includes a chrome-plated brass slide for ultra-smooth throttle pull, plus a throttle assembly and cable to simplify your setup.

🏁 Who It's For:

4-stroke riders who want performance, simplicity, and smooth control — from trail to track, without the complexity of jetting or tuning. Common applications include; Suzuki DRZ 400, DR 650, Honda XR 650, CRF 250, CRF 450, Yamaha YZ250F, YZ450F, WR250F, WR450F, WR426F, KTM 530, KTM 525, KTM 520, KTM 250F, KTM 450F.

Xcelerator Metering Rod

Provides a burst of fuel enrichment when ‘whacking’ the throttle for instant throttle response in all RPM’s. This innovation is a leap in metering rod technology by sustaining the hassle-free, no jetting benefits, while leveling up performance and throttle response. No compromise, just power made easy.

Torque Jet Technology + Power Jet System

The PRO-SERIES combines our newly designed Torque Jet Technology in addition to the Power Jet System. Designed to deliver power exactly where you need it — the bottom-end grunt and wide-open throttle performance is unrivaled. The torque jet design activates at low throttle openings to improve off-idle response and drive out of corners, while the power jet kicks in at higher RPMs to maintain strong top-end fueling without bog or drop-off.

Together, these two circuits and the Xcelerator Metering Rod create an incredibly responsive throttle at all RPM and put real power to the ground without hesitation. Whether you're trail riding, racing MX, or pushing through deep sand, the PRO-SERIES is designed for performance, and delivers.

Internal Fuel Circuits

Fully optimized internal fuel circuit routing, meaning the power jet and torque jet systems are fed through machined passages inside the carburetor body — not external hoses. These fuel passages have been designed to expedite fuel delivery by reducing the required vacuum necessary to pull fuel through each circuit and also shortens the fuel travel path which allows for near immediate fuel delivery. The result, a noticeably quicker throttle response and immediate power transfer to the ground.

By eliminating external fuel hoses, the PRO-SERIES not only looks cleaner but is also easier to install and less prone to hose-related damage in harsh riding conditions.

Tailored Bore Design

Unlike one-size-fits-most OEM carbs, our bore is precision-tailored to match your engine's air volume for sharper throttle response and better power delivery.

It's like a well fitted suit vs one from your dad's closet - mass applied sizing doesn't cut it.

Avoid the pitfalls of generic carbs. Get fitted.

Redirect Slide Ramp

Designed exclusively for our PRO-SERIES & BILLETRON carburetors, this unique slide design does more than control throttle - it redirects airflow to sharpen the fuel signal, delivering quicker, cleaner throttle response and more consistent power delivery across the rev range.

SafeDrain Overflow Bowl

SafeDrain is Lectron’s integrated overflow control system engineered to protect your engine from the complications of fuel overflow in the most demanding conditions. Whether you're navigating steep climbs, hammering through vibration-heavy terrain, or transporting a hot bike after a ride, SafeDrain gives excess fuel a clean exit path and enhanced geometry for improved sealing.

By combining overflow redirection with added venting for incline and decline situations, SafeDrain Bowl ensures stable fuel pressure and consistent performance where other systems fail. It’s peace of mind built into the bowl — no tuning, no fuss, just protection you can trust.

Carb Sizes: Which One is Right?

4T Dimension Template

87mm - 115mm Overall Length
43mm - 48mm Spigot OD
54mm - 62mm Bell OD

Our 4-Stroke Carburetor Kits are engineered to replace a wide range of OEM 4-stroke carburetors, from performance-oriented motocross bikes to dependable dual-sports and trail machines. Available in multiple sizes, these kits cover carburetor dimensions from:
Overall Length: 82mm – 115mm
Spigot OD: 43mm – 48mm
Bell OD: 54mm – 62mm

This flexibility ensures optimal fitment across modern and legacy 4-stroke platforms while delivering massive improvements in throttle response, torque, and top-end power.

Replaces OEM Carburetors Like:

Keihin FCR-MX 37, 39, 41
Mikuni BSR36
Mikuni BST40
Mikuni TM36, TM38
Other 4-Stroke CV and flatside carbs in the 36mm-41mm range
Common Fitments Include:
Suzuki DRZ400-S/SM/E, RM-Z250, RM-Z450, DR650
Honda CRF250R / CRF450R / CRF450X
Yamaha WR250F / WR450F / WR426F / YZ250F / YZ450F / YZ426F
KTM 250-530 EXC/SX-F/XC-F
Other mid-to-large displacement 4-stroke off-road and dual-sport bikes

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FAQ

+ What type of fuel is recommended for 4-Strokes?

We recommend using premium fuel with a minimum octane rating of 91 for all 4-stroke applications. Lower-quality or low-octane fuel can cause tuning issues, poor performance, and starting problems—not just with our carburetors, but with any carb system. For the best results, stick with fresh, high-quality fuel to ensure consistent combustion and optimal throttle response.

+ What's the difference between Lectron carbs and stock/OEM carbs?

Lectron carbs are built for riders who want simplicity without compromising performance.

Unlike stock carbs that rely on jets and constant tuning, Lectron uses a metering rod system that automatically adjusts fuel delivery based the conditions around you (elevation, temperature, humidity, etc..) . No jets to swap. No guessing. Just ride.

Here’s what sets us apart:

No Jetting Required – Adapts to changes in altitude, temperature, and mods automatically.
Smooth, Predictable Power – Strong bottom-end and midrange torque with linear throttle response.
Fewer Parts, Less Tuning – Simpler design means less time wrenching and more time riding.
Built for Performance – Whether you're racing or trail riding, you get better performance without the hassle.

It’s the performance you want, with the simplicity you’ve been missing.

+ What if I need help with install or tuning?

No problem - we've got you covered. Our dedicated support team has extensive experience tuning and installing Lectron carburetors across a wide range of bikes and riding styles. Whether you're working through your initial setup or fine-tuning for specific conditions, we're here to help. Reach out anytime - we'll make sure your carb is dialed in and your bike runs like it should.

+ Will the carb come pre-tuned?

We have over 50 years of experience with tuning carburetors. We setup each carb to a fundamentally determined setting based on information you provide to us. Your carb will be very close or spot on when received. With that said, varying factors like the bikes condition, wear, maintenance, oil ratio, and age of fuel can have an effect with tuning. We suggest a simple, slight tuning at install to achieve max performance and preferability. Once you set it, forget it. Enjoy no-hassle.

Discover more products

My 2008 WRF 250 runs amazing after installing this carb! Easy install as well

The bike runs absolutely incredible and honestly forget sometimes that it's not fuel injected cau...

First impressions even before tuning the carb I noticed instantly that the bike started up way faster than ever before. And with the stock carburetor Id have to pull the choke and or prime kick it a few times. With the Lectron carb I go and turn my key on and the bike starts within a second or two of touching the e-start. And throttle response was crazy good before tuning as well. No more randomly stalling or cutting out when it was semi cold and doing an almost WOT acceleration. Then after tuning it with the a few email interchanges between Tommy and I Tommy was able to tell me exactly what it needed in order to run cherry. I've never ran or ride a bike with a Lectron carb but after getting a few bugs out the way and can firmly say I 110% percent stand behind these guys and will always use their products and support their products. The bike runs absolutely incredible and honestly forget sometimes that it's not fuel injected cause it runs insanely good. Best thing I've done to my Ktm and plan to do it to my yz125 as well. And I can't thank Tommy enough for all the help and the 15 plus emails that were sent, Tommy's an awesome dude and really appreciate him.

1 day to install and tune, i'm good to go

i have an older 2001 DRZ 400 with a large aftermarket fuel tank and a yoshimura exhaust, with the air box opened up for fun, elevation doesn't affect 4-strokes as much but when i i can go from 100' to 4000' in a day of riding its something to considerinstallation was very easy considering that its smaller than a flat side pumper carb, and the bike ran right away, it was a little rich at the start but like any new carburetor it needed to be tuned to my bike and thats where the big difference for me was.the process of tuning my old carburetor took about 2-3 hours to make a change depending on how much of a struggle the intake boot would be, i would have to take off the seat and fuel tank, part of my luggage rack, and exhaust brackets ao i could move the sub-frame te get enough room to get the old carb out of the bike and get the the jets in the float bowl (to spare you the details i couldn't simply rotate my old carb to get access, it HAD to come off), and that was for every adjustment, the old carb was too close to the starter to even get to the air mix screw, it was not fun.now onto the Lectron, i needed the remote choke for my bike due to the larger fuel tank, if your wondering if you need one for your bike just go over it and see if you can easily reach the top of your carb, if you can then you probably dont need it, lectron doesnt list a remote choke for my carb but the sales team contacted me quickly and we worked it out, (it works great BTW), i didn't end up using any of the brackets they sent and isted just tuck it behind the frame.tuning, the important subject here, it couldn't be easier with the lectron, i dont even need to get off the bike to make the small adjustments, i just pull off to the side of the road, give a knob a little twist and im back back on the road again literally 5 seconds, and when i had to do a "major" adjustment i just pulled the tank off (i only need to because of my aftermarket one im sure with a stock tank i woulnt even need to do that) loosen the carb boots so i can rotate the carb and thanks to the easy tune kit i bought with the carb i dont need any more tools to pop off the slide cap, adjust the metering rod and put it back together, its a 30 minute job for a "major" adjustment, and thats only because of my aftermarket fuel tank, if it were a stock one im sure it would be 5 mins tops.in the end if your racing your dirt bike and want every last possible ounce of performance and have hours or days to kill, a shop to work on it in not to mention all the different jets you might need to tune it, then a pumper carb might be for you, but if your like me and just want to go have fun on your bike get a lectron it took 1 day to install and tune and im good to go.

I never want a non-lectron carb again

Ive heard the hype around the lectron carb for about 7-8 years and as someone who works on power sports as a side job, Ive messed with a few bikes that had these carbs from 2 stokes to 4 strokes bikes and four wheelers. I never did get one till about a year ago and coming from a guy who had rebuilt and tuned hundreds of stock and aftermarket carbs, I never want a non lectron carb again. Adjustments are super easy, even the slide adjustment can be made in less than 5 minutes. Your bike will run smoother and crispier with throttle response like no other. I was a little skeptical about the metering rod technology at first, but Ive yet had to adjust anything at different elevations. Great product thats worth every bit of the money.

2007 DRZ400SM

I had a few issues getting the carb in. Not anything with Lectron. I am just a bit OCD and removing the back frame enough to pull the boot to the engine and air box wasn't giving me enough space to pull them back on all the way. So I removed the whole back frame and drilled 4 holes I'm the Air box and it looks amazing. Was having a few issues with getting the bike started after it was installed so I called Lectron and Hunter was very helpful and told me the setting for the idle screw they had on their bike and waited for me to take an engine bracket off and remove the gas tank to adjust the metering rod. And I let the bike cool down and start it a couple times and it works way better than the stock mikuni carb it had in it.

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