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Lectron Carb - Test, Tune and Review, KTM 330 SX
Hey everyone,
The folks at Lectron Fuel Systems have provided us with a couple 38MM Carbs for project builds, testing and review. There has been a lot of people shopping for alternatives to their OEM Keihin carburetors. I have personally been asked repeatedly about detailed info on this Carb. As we move through the over-view and into tuning and testing, I hope to answer a lot of those questions.
First off, It is a cast, vented, flat slide carburetor that utilizes a metering rod combined with a power jet to make up three individual fuel circuits. There is no jetting required. The first two circuits distribute fuel via the grind in the fuel rod. This rod has two separate grinds depicted by two numbers stamped onto the rod. The first number is relative to approximately 3/8 throttle through the rest of the stroke to wide open throttle. The second number is relative to the idle circuit and just off idle throttle response. The third circuit is the power jet that begins gradually applying fuel at approximately 5/8 throttle to wide open.
The way to look at these three is to break them down starting with idle, the second number on the metering rod, the idle circuit. Let's say for example we have a 3-2 metering rod. The smaller numbers are leaner and the larger numbers, richer. We first start and warm the engine up to operating temp. Once there, we adjust for idle. Once idle is set we can blip the throttle a few times and evaluate our idle circuit. If the slide height is high, ideal is about the thickness of a penny, if it is considerably higher than that we are probably a bit rich. An elevated slide to achieve idle indicates the need for "more air" to achieve the optimum AFR therefore we should consider a rod one step leaner on the second number. That same condition would also likely result in a sluggish response off idle. If the second number is too lean you will experience a very low slide height to get any idle. A paper thin slit for slide height. The off idle response would be a hollow , empty blaaaw, followed by erratic acceleration. You will also experience the inability for your bike to "settle down" after a couple rev's. It will be zingy and nervous not wanting to settle back to idle.
Again for example, lets say we have done that and idle is clean with a low slide height, and throttle response is quick and crisp. Our second number is set. It is "2". The first number comes into play just past quarter throttle. While riding, your idle and off bottom remain excellent, but you have that familiar mid range burble and lack of strong acceleration. That indicates a rich condition, you then need a metering rod with the first number being one number smaller. However, if your mid is clean, but "hollow" and lazy, you are likely lean and need one number bigger on that first number.
You now have your fuel metering rod. In this case, it's a 3-2. Now we can tune the wide open throttle fuel. The WOT position allows fuel to be drawn from the power jet supplementing fuel at WOT. You will notice in the picture of the slide 1/2 raised, it is at the bottom of the brass piccolo tube. The tube is approximately 1/2 way down the diameter from the top. The length of the tube determines "when" fuel is delivered, and the size of the power jet determines "how much". When the slide rises to the bottom of the tube, you start getting extra fuel. In this case it is approximately 1/2 throttle. As the slide rises to WOT the vacuum is drawing it's max flow of fuel.
You do not have to adjust the power jet piccolo tube length. They come pre set. Also the fuel rod and slide height come set for your application from the factory. They arrive real close to spot on. I don't want you to think you have a lot of tuning to do. This is simply an overview of the Carburetor and how it supplies fuel. They came pre set very close and minor tuning changes are a breeze.
Our Carb heat collar installed beautifully. I indexed the set screw at the 9 o'clock position. Notice the 3 o'clock position has a small hole in the bell of the carb. That hole is your choke circuit. You don't want to push in the wall outside that hole with the set screw.
Remember when tuning, always tune by doing plug checks and validating your readings with electronic aids like AFR or EGT sensors. If you are not comfortable doing it your self, there are a lot of people and resources to help get you dialed in.
Stay tuned. We will be following up with discussions and videos. The first test bed will be on the KTM 330 Mod Bike.
Hey everyone,
The folks at Lectron Fuel Systems have provided us with a couple 38MM Carbs for project builds, testing and review. There has been a lot of people shopping for alternatives to their OEM Keihin carburetors. I have personally been asked repeatedly about detailed info on this Carb. As we move through the over-view and into tuning and testing, I hope to answer a lot of those questions.
First off, It is a cast, vented, flat slide carburetor that utilizes a metering rod combined with a power jet to make up three individual fuel circuits. There is no jetting required. The first two circuits distribute fuel via the grind in the fuel rod. This rod has two separate grinds depicted by two numbers stamped onto the rod. The first number is relative to approximately 3/8 throttle through the rest of the stroke to wide open throttle. The second number is relative to the idle circuit and just off idle throttle response. The third circuit is the power jet that begins gradually applying fuel at approximately 5/8 throttle to wide open.
The way to look at these three is to break them down starting with idle, the second number on the metering rod, the idle circuit. Let's say for example we have a 3-2 metering rod. The smaller numbers are leaner and the larger numbers, richer. We first start and warm the engine up to operating temp. Once there, we adjust for idle. Once idle is set we can blip the throttle a few times and evaluate our idle circuit. If the slide height is high, ideal is about the thickness of a penny, if it is considerably higher than that we are probably a bit rich. An elevated slide to achieve idle indicates the need for "more air" to achieve the optimum AFR therefore we should consider a rod one step leaner on the second number. That same condition would also likely result in a sluggish response off idle. If the second number is too lean you will experience a very low slide height to get any idle. A paper thin slit for slide height. The off idle response would be a hollow , empty blaaaw, followed by erratic acceleration. You will also experience the inability for your bike to "settle down" after a couple rev's. It will be zingy and nervous not wanting to settle back to idle.
Again for example, lets say we have done that and idle is clean with a low slide height, and throttle response is quick and crisp. Our second number is set. It is "2". The first number comes into play just past quarter throttle. While riding, your idle and off bottom remain excellent, but you have that familiar mid range burble and lack of strong acceleration. That indicates a rich condition, you then need a metering rod with the first number being one number smaller. However, if your mid is clean, but "hollow" and lazy, you are likely lean and need one number bigger on that first number.
You now have your fuel metering rod. In this case, it's a 3-2. Now we can tune the wide open throttle fuel. The WOT position allows fuel to be drawn from the power jet supplementing fuel at WOT. You will notice in the picture of the slide 1/2 raised, it is at the bottom of the brass piccolo tube. The tube is approximately 1/2 way down the diameter from the top. The length of the tube determines "when" fuel is delivered, and the size of the power jet determines "how much". When the slide rises to the bottom of the tube, you start getting extra fuel. In this case it is approximately 1/2 throttle. As the slide rises to WOT the vacuum is drawing it's max flow of fuel.
You do not have to adjust the power jet piccolo tube length. They come pre set. Also the fuel rod and slide height come set for your application from the factory. They arrive real close to spot on. I don't want you to think you have a lot of tuning to do. This is simply an overview of the Carburetor and how it supplies fuel. They came pre set very close and minor tuning changes are a breeze.
Our Carb heat collar installed beautifully. I indexed the set screw at the 9 o'clock position. Notice the 3 o'clock position has a small hole in the bell of the carb. That hole is your choke circuit. You don't want to push in the wall outside that hole with the set screw.
Remember when tuning, always tune by doing plug checks and validating your readings with electronic aids like AFR or EGT sensors. If you are not comfortable doing it your self, there are a lot of people and resources to help get you dialed in.
Stay tuned. We will be following up with discussions and videos. The first test bed will be on the KTM 330 Mod Bike.
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