PRO-SERIES Four Stroke Tuning Guide

Lectron has been designing and manufacturing simple, high performance fuel systems in the United States since 1974. With a rich history in practically all divisions of two-wheeled motorsports, we are proud to have you as a part of our legacy.

 Lectrons outflow comparably sized carburetors while delivering fuel in a more finely atomized form. This creates better throttle response and more horsepower, all while staying in tune throughout a wide range of elevations and temperatures. Instead of rejetting throughout the day, you get to spend more time riding.

Each metering rod has a specific grind profile that has been pre-selected for your application. 

Tuning Spark Notes: 

Please read detailed tuning instructions later in this manual

1. Tune your rod first. If you have to turn your idle screw more than 0.5 turns either way, you may need to adjust your rod! Only tune the rod for idle and off idle response, and always reset your idle screw back to the starting setting when adjusting the rod.

2. Tune your Torque Jet second (bottom screw). This controls fueling from just off idle through half throttle. Tune this circuit for best response in that range.

3. Tune your Power Jet last (top screw). This controls fueling from half throttle to full throttle. Tune this circuit for best response in that range, and best peak power. 

 

Disclaimer: Lectron products come preset with a base tune determined by in-house testing, rider feedback, and other research. Each application can be influenced by external factors resulting in necessary tuning. Examples of these factors are: riding style, local fuel, custom engine work, etc.

Lectrons are mechanical fuel systems that use physics to compensate for a wide range of elevations and temperatures as well as humidity and other factors that effect air density. They DO NOT mechanically change their own tune and cannot sense load. 

For extreme environment applications like dune riding, snowbiking, ice racing, Supermoto, or other related activities under variable loads, you may need to make tuning changes.  

These are general steps and guidelines for installing your new Lectron carburetor. The actual steps you take may vary. 

 

Step 1: Prepare the Bike

• Turn your fuel off and disconnect the fuel line from the carburetor. 
• Drain the bowl if there is fuel in it. 
• Remove the seat and fuel tank. 
• Loosen up the center subframe bolt(s) and remove the lower subframe bolts. 
• Loosen the hose clamp on the air box side of the carburetor.

Step 2: Uninstall the Carburetor

• With the subframe rotated upwards, loosen the hose clamp on the engine side of the carburetor and remove it from the frame.
• If your carburetor has electrical plugs attached to it, disconnect them. Tape or heat shrink the ends up to keep dirt out, and zip tie the plugs out of the way (usually to the frame up under the gas tank). 
• Disconnect the factory throttle cable from the slide or push-pull rotor. If its has a throttle slide, you will need to collapse the spring against the top cover in one hand, and push the throttle cable in, then outwards and it will come free. 
• Thread the top cover off of the factory throttle cable if it has one, and remove the OEM throttle cables/throttle tube assembly.

 

Step 3: Install the Top Cover, Gasket, Spring, and Slide

• Install the supplied throttle tube and cables, be sure to route the cable such that it will not be pinched when turing the bars
• Thread the Billetron top cover all the way onto the throttle cable. Do not completely tighten this as you will need to orient the front of the top cover to face the front of the bike. 
• Install the Billetron top cover gasket and spring onto the cable.
• Collapse the spring up against the top cover so the cable is free, then insert the ball end of the cable into the opening on the face of the slide. Release the spring into the hole on the slide as pictured. 

Step 4: Install the Billetron

• Seat the spigot of the Billetron into the intake flange, leaving the hose clamps loose. If the carburetor does not fully seat, you may need to trim the locating tabs off of the flange.
• Route the vent lines down by the shock. If you choose, you can route one or two vent lines up towards the frame or into the airbox. Do not restrict the vent lines with wire or zip ties, or route them into an unvented catch can.
• Confirm that the slide is open no more than 1/8” in the bore of the carburetor. If it does not close enough, thread your cable adjusters together first. 
• If you still do not have enough free play, remove the lock nuts from the carburetor side first, and the throttle side if necessary. 
  
   Note: Starting the bike on a metal stand on a concrete floor can cause excessive vibration and make the carburetor overflow.

First Start

• Turn on the petcock and watch the float bowl fill with fuel. There should be a small air pocket in the top right corner of the float bowl.
• Pull the choke and fire the bike up. 
• You may need to blip the throttle to keep the bike running as these chokes are very rich. 
• Run the bike for a few seconds on the choke, then turn it off. 
• Continue lightly revving the bike until it is up to operating temperature. 
• If the bike is making an unusual noises, pinging, revving uncontrollably, or anything that may indicate an issue, turn it off immediately.
• Once the bike is up to operating temperature, take it for a nice, easy test ride. Listen for any indications that it could be running too lean or too rich and adjust as necessary. If you are unsure which way to go, always start going richer first. 

IF THE BIKE WILL NOT START

• Pull the spark plug and see if it is wet or dry.
• If it is dry: Take 3 vent lines in one hand and cover them with your thumb. Lightly blow in the 4th one and it will force fuel up the power jet line and into the bore of the carburetor. Continue trying to start the bike. If this is the only way your bike will start,  check for spark and proper compression. A leak down test is an easy way to confirm that the bike is generating proper vacuum to the carburetor and there are no air leaks.  If no leaks are present, this is likely from a lean condition, assuming there isn't another issue present. This method for starting is NOT meant to be a permanent solution. 
• If it is wet with fuel: Install a fresh spark plug and continue trying to start it. If it will not start after a few cycles, hold the throttle wide open and try to start it. If it still will not start and the plug is wet again, refill the tank with fresh gas, confirm the air filter is clean, and try again. Further troubleshooting steps include checking the stator and coil for proper output. 

Setting Cable Free-play

• Once the bike is up to operating temperature, make sure the bike is not loaded up and set the idle to 1600-1900 RPM. 
• Back the cable adjusters out JUST until you hear the idle RPM begin to increase. 
• Thread the adjusters back in 3-5 turns and lock them there. 
• If your cable adjuster at the throttle has too many threads showing or will not achieve the proper amount of free-play, use the other adjusters on the cable or at the top of the carburetor to do so. 

Tuning Basics

 Due to the proprietary nature of our carbs, the tuning methodology differs somewhat from traditional carburetors. The following steps should be taken in order to achieve the desired carb settings.

• Set idle: The bike must be up to operating temperature before setting the idle. Lectron Carbs respond best when the slide is set at 0.068” from fully closed and are set to this distance from the factory. Please reference your invoice for the number of turns from all the way in on the idle screw to return to if needed. This corresponds to a fairly high idle (1600-1900 RPM on most bikes), which is completely normal. To start, adjust your idle screw up to ½ turn in either direction to try to achieve the desired idle. If the desired idle cannot be achieved within that adjustment range, the rod will need to be adjusted.
  • Make sure your throttle has enough free play if the idle is high and the idle screw has no effect.
• Adjusting the rod:
  • • Adjusting the rod clockwise (right) makes it richer, adjusting it counterclockwise (left) makes it leaner. 
    • Adjust your rod for the best idle and off idle response, use the symptoms below to guide you on which way to go 
    • Turn the rod without pushing it into the slide to make your adjustment, then push it into the slide to reorient the flat side to face the engine. It is critical that the flat side faces the engine.
    • Be sure to reset the idle screw back to the starting number of turns for every rod adjustment.
    • Generally working in ¼ turn adjustments works best for normal adjustments, and working in half turn adjustments works best for large adjustments.
    • If you have to go more than 2 full turns on the rod from the starting position, there may be an issue with your bike, please contact us for more advice.
    • Lean rod symptoms
      • Hesitation off idle
      • Lack of power off idle
      • Hanging idle
      • Does not like large changes in throttle position
      • Hard to start when cold (usually)
      • Engine gets hotter than normal
      • Excessive popping on decel (some decel burble is normal)
    • Rich rod symptoms
      • Very low idle
      • Smell of unburnt gas at idle. 
      • Backfiring thru the intake when blipping the throttle off idle
      • Hard to start when hot (usually)
      • Top end power is flat
      • Poor fuel economy
    • Tuning with an AFR probe/sensor:
      • The goal is to set your rod so that you have an idle AFR between 12 and 12.5 for optimum responsiveness 
      • As stated above remember to reset your idle screw every time you adjust your rod and readjust the screw afterwards
      • When adjusting the rod, these guidelines may be helpful:
        • AFR > 15 go 1 turn richer
        • AFR> 14 go 3/4 turn richer
        • AFR> 13 go 1/2 turn richer
        • AFR> 12.5 go 1/4 turn richer
        • AFR< 12 go 1/4 turn leaner
        • AFR< 11 go 1/2 turn leaner
        • AFR< 10 go 1 turn leaner
        • Idle AFR over 13 may pop on decel
• Adjusting your Torque jet
  • On our 4 stroke carbs the Torque jet serves as an enrichening circuit at middle throttle positions at medium cruising speed. The starting screw position is 1/8th turn from all the way in.
  • Adjust this circuit in very small increments, no more than 1/8th turn
  • Richen this circuit if your bike lacks power in the midrange or runs hot at cruising speed
  • Lean this circuit if you have poor fuel economy, power falls flat on top, or you smell excessive unburnt gas when cruising. You can fully close the circuit if necessary
  • If tuning with an AFR gauge, you should see AFR’s of around 13 for light loads and AFR’s around 12 for medium loads
• Adjusting your Power jet
  • On our 4 stroke carbs the power jet serves as an enrichening circuit at half to full throttle at high RPM. The starting screw position is 1/8th turn from all the way in.
  • Adjust this circuit in very small increments, no more than 1/8th turn
  • Richen this circuit if your bike lacks power wide open or runs hot at highway speed
  • Lean this circuit if you have poor fuel economy, power falls flat on top, it feels like the bike is cutting in and out at high rpm, or you smell excessive unburnt gas when at over half throttle and at high speed.  You can fully close the circuit if necessary
  • If tuning with an AFR gauge, you should see AFR’s at 12 +/-0.5 when running through the gears at WOT or cruising at high speed.
• Cold start procedure 
  • Kick start 
  • Turn your petcock and choke on. Slowly turn the bike over 3-5 times to prime it.
  • Kick it once with the choke on while giving it no throttle. It should fire for a second and shut off, it is now fully primed. 
  • Now turn the choke off and kick again with no throttle. When it fires, you may need to hold the revs around 2500-3000 with the throttle to keep it running for the initial warmup. You may not need the choke depending on how cold it is and the state of your tune. You may also be able to turn the choke off during step 2 before it shuts off depending on the bike
• E-start
  • Turn your petcock and choke on. 
  • Press the start button without giving it any throttle at first. When it fires, turn the choke off immediately. you may need to hold the revs around 2500-3000 with the throttle to keep it running for the initial warmup. 
  • If it takes more than a few seconds to start, try slowly modulating the throttle between 0-1/4 throttle. You may not need the choke depending on how cold it is and the state of your tune. 
• Troubleshooting
  • Please ensure that your bike is fully mechanically sound! Low compression, valve clearances, cam and ignition timing, air leaks, and air filter condition will all effect the tuning of your carb and may make it more difficult to tune
  • To get the best performance out of our carb, we recommend opening up the airbox as much as you feel comfortable depending on the type of riding you’re doing. Beware of water crossings if you leave the airbox cover off.  
  • Hard start – Hard starting is usually from too lean of a rod setting. You can prime the carb by plugging three of the vent lines and blowing in the 4th. This is a temporary solution to get the bike running for further tuning. If the bike is hard to start when hot the rod setting may be too rich. Avoid giving it throttle on hot starts!!
  • Low idle/wont idle - usually a very low idle means your rod is too rich. Follow the rod tuning instructions above
  • Slide stiction – remove your slide and make sure the metering rod slides smoothly in the pickup tube and is free of burrs. You can lightly deburr the rod and slide with scotchbrite if the issue persists. Make sure that you are not confusing this with a hanging idle from a lean rod condition
  • Flames outs – Flame outs are usually from too lean of a rod setting. Please refer to the rod tuning section
  • Flat top end power – this is usually a symptom of being too rich on any of the three circuits. Lean the power jet first, the torque jet second, and the rod last.