2 Stroke PDF Bank:
Basic Starting Settings for 2 Stroke Dirt Bike Carbs Running Standard Fuels
Below is a number of turns that will get your rod set to a basic, ballpark, starting setting. Further tuning should be expected. If you want the exact starting length of your stock rod, you will need to call or email us with your serial number (engraved on the engine side of the carb or the slide) and the rod number installed.
To start, thread the rod into the slide just until there aren't any more visible threads on the rod. Continue turning the rod based on the spec below. Once you have reached that point, press the rod into the slide to collapse the spring, and rotate the rod to where the flat side will be facing the motor.
Rods Turns in
Turning it to the left lowers your slide height and your idle. Turning it to the right raises the slide height and your idle. If you adjust your idle too far down and the screw locks up, reach inside your carb, raise your slide up, and turn your idle screw clockwise until it catches again. If you lean out your rod, you will have to turn your idle down, and if you richen your rod, you will have to turn your idle up. Wait until your bike is warmed up and clears out before adjusting your idle.
The metering rod is used in combination with the vacuum from the motor pull fuel from the float bowl. The flat side must always be facing the motor to do this. Don’t adjust it without running it first. It comes preset from the factory, and tuning it on the stand will not accurately represent conditions when the motor is operating under load at the track or on the trail.
To tune the rod, remove the slide and hold the slide to where the rod is pointing towards you. Turning it to the right will richen it. Turning it to the left will lean it. What you are doing is either threading it in and shortening the length of it (.006” per ¼ turn), or threading it out and adding length to it. Then, push the rod in towards the slide to collapse the spring and turn it back to where it is facing the motor to save your setting. You can use a set of calipers to measure the length of the rod and get back to the starting point (on your invoice).
The power jet is used to fine tune your top end and works like a faucet. If you turn it to the left, it opens the valve and richens it. If you turn it to the right, it closes the valve and leans it out. Tuning this has nothing to do with your idle or low to mid-range throttle response. NEVER ride with a closed power jet. If you are riding dunes, deep sand, outdoor motocross, or snow where you are wide open for extended periods, we recommend going ¼ turn richer to keep your motor cool. The fuel level in the line will be even with the level in your float bowl until the power jet is activated.
Cracking the throttle open is not enough to activate the power jet. The motor must be pulling a sufficient vacuum with the slide height over the bottom of the jet nozzle for about a second. Trying to activate it on a stand will usually not work because it is not under enough load to pull enough of a vacuum before revving out.
Most two stroke dirt bikes running pump gas will come with the power jet open between 3/4 of a turn and 1 1/4 of a turn from bottomed out.
Trouble Shooting and Basic Tuning
While we do set the carb to the best of our ability from the factory, some additional tuning may be required based on where your ride, your riding style, how fresh or worn out your motor is, and what mods you've done. Changing fuels may also require some minor adjustments depending on the quality of fuel. Changing from pump gas to oxygenated race gas will often require purchasing a richer rod.
Remember that you are shooting for a "sweet spot" when tuning the Lectron. It is often a window that ranges about 1/2 turn inbetween being too lean and too rich where the power the strongest and the throttle response is crisp. By making large adjustments, over 1/2 turn at a time, you risk missing the sweet spot and going from too lean to too rich, or vice-versa. This is why small adjustments are always recommended. Some overly rich symptoms often overlap those of a lean condition, and make diagnosing it difficult. If you find yourself lost, your starting length is on your invoice and we keep it on file.
Never tune on the stand. Trying to tune a motor that is not under a load won't accurately represent the changes in the field. Lectrons pull fuel much more quickly than a traditionally jetted carb, so if you rev a bike that is under no load on a stand, it is typically going to sound rich because the motor is loading up on fuel. By going leaner and eliminating this, you will be out of adjustment when a load is put on the engine.
Lean symptoms in two stroke dirt bikes include bogging or gagging and falling flat on its face when you crack the throttle, not running unless the choke is on, or having very harsh transition from a weak mid range to strong top end. Adjust your metering rod. Cracking the throttle is not enough to activate the power jet, so do not adjust it.
If you are riding on the pipe and your bike feels flat, down on power, or excessively "pingy," your power jet may be lean. Open the power jet 1/8 or 1/4 of a turn. A standard dirt bike should not need a power jet that is open more than 1 1/4 turns. If you are riding a snow bike or dunes where you are wide open for extended periods of time with excessive load, you may need to go to 1 3/4 turn open, but not more than 2. Dirt bikes running gasoline will never need a larger power jet.
A rich two stroke will often stutter or fell blubbery before taking off, it could smoke more than normal depending on your fuel mixture, or load up at low RPM. The RPM returning to idle when you close the throttle quickly will often sound choppy, dropping down, then hitting high, before dropping back down. We never recommend tuning around this if the bike is otherwise running well because engine performance is determined on accel, not decel, however, it can usually be minimized by going 1/4 turn leaner on the rod. This is the same for "pipe bang" when riding down a road (the bike loads up when pulling a large vacuum at a low throttle position in a high gear, then burns off the excessive fuel incosistently).
One thing to keep in mind is Lectrons are performance products that deliver fuel in a different manner than a traditional jetted carb. The sound is typically "fuller" vs. "fluffier." The difference is sound is often confused with a difference in performance, especially for a throttle position that will not affect the actual riding characteristics of the bike (closed throttle position or 1/10th open). Sound can often be taken into consideration when tuning, but should not be the sole reason for an adjustment.
Frequently Asked Questions
Q: How do I route my vent lines?
A: If you are running two vent lines, you can run one into your air box or to the top of your frame, and one down to the swing arm. If you are running a “T” set up, you can run two up high, and one down to your swing arm. No matter what, you need at least one running down below your carb.
Q: Why is my bike bogging?
A: If you whack the throttle open (going from idle/low rpm to mid-range), and the motor gags like it wants to die, your rod is most likely too lean. If it gurgles or stutters, it is too rich. Adjust it in ¼ turn increments.
Q: Why is my top end flat?
A: If you are running wide open and your bike feels flat, turn out (richen) your power jet in 1/8th turn increments until it runs how you want it to. If it stutters or gurgles, turn in (lean) your power jet 1/8th turn increments.
Q: Why is my bike hard to start?
A: Use your choke if it is cold. If it is hard to start hot, your metering rod could be lean. Adjust it ¼ turn richer, and see if it starts and runs better. If you believe your choke is not working, prime the carb by plugging one vent line and blowing in the other until you see a small amount of fuel go through the power jet line, start the bike and, once it is running, pull the choke up. The RPM should fall dramatically.
Q: If I see smoke and spooge, do I need to lean it out?
A: Certain brand oils and mixture rates smoke and spooge more than others. Tune it for the best performance, not the least amount of smoke.
Q: Should I change my oil mixture?
A: Each oil is engineered differently. Mix your oil according to the oil manufacturer’s specs.
Q: Why does my bike sound rich, but run great?
A: Metering rod carbs draw fuel differently and sound different from a jetted carb. Tune for the best performance, not the best sound.
Q: Why does my bike run with the choke on, but not with it off?
A: The choke works to richen it up. If it only runs with the choke on, your bike is way too lean.
Q: Why is there air in my fuel line?
A: All fuel lines will have some air in them. The difference is now you can see it in our transparent lines and you couldn’t in the black line.
Q: My carb has Allen screws. What size are they?
A: The top cover Allen screws are 7/64”. The bowl screws are 5/32”.
Q: I'm going to a high compression head, what do I need to change?
A: Try riding it with your current settings first. Minor rod tuning may be required based on how aggressive the head is.
Q: I'm taking my Lectron off bike "Y" and putting it on bike "Z." What do I need to change?
A: As long as the bike is the same CC class (125/150 or 250/300) you will be fine UNLESS it is going to a YZ (They run a shorter bell) or to a 2017+ KTM (balanced motor - must run 38HV).
Q: What is the starting length of the rod for my carb?
A: Rods are mechanically ground and zeroed before we calibrate them to match your build. This means each rod will have a different starting length and will vary based on the batch and what we think is a good tune for you based off your specs. They are always measure from the tip of the rod to the brass ring on the slide insert in inches (to the thousandth). Do not collapse the spring when measuring.The starting length can be found based on the carb serial number if ordered from a supplier, or if ordered directly from Lectron, it will be on your invoice and stored electronically in our system, however, we do have a method below that will get you in the right ballpark.