Here is some info from OMW`s Mr.HP Eric Oldham - some of it "may" be DS & 4 stroke specific, but most can be applied to any/all Lectron tuning.
Lectron Carburetor Instructions
Please read these instructions before calling. We are happy to answer your questions, but most questions are answered here.
1. The choke is vertical on the front half of the carb body and has an acorn nut on top. Push fully down to turn off. The choke rarely has to be used on Lectron carbs. Ensure it is fully off when tuning the carb.
2. The idle is the horizontal screw on the side of the carb with a spring behind it. Screw in for higher idle. If idle cannot be achieved by screwing in all the way, open the air/fuel idle bleed. If still cannot achieve idle, lean out the metering rod (needle) ½ turn.
3. The air/fuel idle bleed is the vertical screw in front of the idle screw, but behind the choke. Screw out for leaner smoother idle (max 3 turns). Screw in to richen if experiencing bog or hesitation when the throttle is snapped open quickly
4. The power jet is on top of the back ½ of the carb, between the air bell and the slide. It is located under a screw. This is for wide open top end tuning only, although, if it is extremely lean, it can affect the throttle snap. If the optional adjustable power jet is installed it has a sprung adjustment screw- max adjustment is 2 turns out- screw may fall out beyond this. 3 jet sizes is about 1 on a normal main jet.
5. The metering rod (or needle) screws into the nylon insert of the slide. Adjustment is made by screwing in for richer setting, or screwing out for leaner setting. After setting desired length, the spring loaded needle/nylon insert must be pushed up and rotated to ensure the FLAT SIDE OF THE NEEDLE IS FACING THE ENGINE. This DOES NOT change the actual needle setting.
6. The float needle seat is inside the float bowl and allows gas/alcohol into the carb.
1. After installing your new carb, check throttle cable for binding, for being seated properly in the adjusters, and for full open and closed throttle positions by looking through the back of the carb with air filter off. Always leave approx 1/8"- 1/4 of slack in the cable (this means you should be able to push the throttle a little before it engages the cable and slide- LACK OF SLACK IS THE PRIMARY CAUSE OF PERCEIVED THROTTLE HANG AND INCONSISTENT IDLE. Check the throttle assembly for smooth operation. With the motor running, out of gear, and parking brake on, check for cable bind by turning the handlebars full left and right, then move the cable around by hand and ensure engine RPM does not change- if it does, you do NOT have enough slack. Cable routing is critical- do not put sharp bends in the cable- smooth continuous bends are a must. REREAD THIS PARAGRAPH- IF THE CABLE IS IN A BIND, IT MAY NOT RETURN TO IDLE! IF THE CABLE HAS TOO LITTLE SLACK, THE SLIDE WILL NOT RETURN TO IDLE: JUST 1/8 in OF LIFT ON THE SLIDE WILL SEND THE MOTOR TO REDLINE AND DECEIVINGLY SEEM TO BE STUCK WIDE OPEN!! Ensure the cable is not binding in the throttle adjuster slit as you open/close the throttle (rotate adjuster 180 degrees if necessary). If the cable wire is rubbing in the slit, you will experience hard throttle pull and it may not return to idle easily.
2. Do NOT let gas sit in the float bowl for over a month- it will start to varnish and cause operational and performance issues. If your engine was running fine the last time you rode it, but now acts strangely- do not automatically start retuning on the carb. The carb is always the first assumption, but usually a wrong one. Something has changed, but not likely the tuning of the carb. If the bike has not ran in over a month, it could be stale gas. Even longer periods of storage can result in varnish in the carb passages- the carb doesn't need retuned- it needs thoroughly cleaned out.
3. Use a set of high quality dial calipers to measure the needle length after any adjustment and never exceed 2.075 longest, or 1.969" shortest setting on a 46hv (2.000 on 48hv)- measuring from the brass insert to the tip of the needle. Exceeding the shortest setting will cause the needle to lift out of the carb body at full throttle, thus sticking the throttle wide open. If you are close to this setting or you are unsure, remove the air filter and tug on the needle while holding the throttle wide open (with the engine turned off!). If it comes out of the carb body, you are at an unsafe position. If either of these extremes are met, and satisfactory tuning cannot be obtained, double check everything, then contact your dealer- the needle will have to be changed. Note: The idle will change after any needle adjustment- readjust the idle with the IDLE SCREW.
4. As with any carb and throttle setup, use weather boot protectors at each cable end to keep dirt/sand out of throttle housing and carb slide. In mud or fine sand, use heat shrink and/or silicone anywhere there is an opening to a cable, including the midway adjuster. Also use a foam air filter with an outerwear protector, especially in sand and dusty conditions to keep grit from obstructing and scarring the slide. We do not recommend K/N. No-Toil brand performs and filters better (it will also require more power jet). IMPORTANT: Block off the opening into the side of the snorkel tube after removing the stock vacuum line!
5. This IS NOT a CV carb. Due to large vacuum on the slide from large 4 stroke engines, when the engine is running, the throttle may exhibit somewhat more resistance at idle until the vacuum is broken, ESPECIALLY IF THE NEEDLE SETTING IS TOO LEAN! Richen the needle to alleviate this problem. This is normal on this type carb. This resistance should NOT be present with the motor off, if so, check all of the above mentioned cable precautions.
6. Please double check your setup and routing. Almost all problems are found to be from incorrect installation. If your throttle appears to be hanging, your carb is NOT likely the problem- it is a cable, cable routing, or throttle issue. Check throttle for smooth operation by itself, then attach cable without the carb and check again. This should narrow down the problem. We recommend pressure lubing your cable with a cable luber kit after every ride in dusty/sandy conditions on any carb.
7. A tether kill switch is highly recommended on all modified atv's- it may have more power than you are used to, especially at low rpm.
8. If you choose to dyno your bike on knobby tires, the dyno may actually read lower hp and torque numbers, especially at lower rpms, due to the significant increase in torque and acceleration spinning the knobby tires harder than on the stock carb. For accurate results and tuning, always use a good quality flat track tire, such as Hoosier, McCreary, or American Racing.
1. Always start with a known good engine with new spark plugs and sufficient compression. If it didn't run correctly before, it still won't with this carb. If you replace more than one item, such as during a rebuild, we highly recommend you start your engine on the stock carb. Poor performance due to incorrect engine assembly is always blamed on the new carb and can frustrate you and us for a long time.
2. After you have installed the carb, recheck the safety precautions in the previous instructions. Also, double check intake clamps are tightened (retighten after first heat cycle), shop rag out of the intake, air filter and boot in place and tightened, intake o-rings remained in place while installing intake (use grease to hold in place), with no air leaks.
3. Best performance and idle characteristics are achieved with a snorkel tube (NOT a direct mount filter), and no air box.
4. Before tuning, make sure the float bowl level is sufficient. Float bowl level affects tuning drastically.
5. Make sure your carb was purchased for your exact setup. Porting can drastically change your carb tuning (not necessarily richer or leaner) - it is difficult to pre-tune for a ported engine. If you change from snorkeled air filter to a direct mount air filter, do not expect your carb to run. This drastically changes the fuel requirements. Direct mount air filters require 4-5 sizes leaner needle.
6. Make sure the intake manifold opening is as big or bigger than the carb outlet. Improperly ported intake manifolds cannot be tuned correctly with this carb. Make sure the carb opening is butted up to and touching the intake manifold- too long of an adapter boot can cause tuning problems by allowing fuel to fall out of suspension and pool between the carb and intake.
7. Tuning must be done with engine at operating temperature. Engine will be slightly lean (i.e. poor throttle response) until sufficiently warmed up. DO NOT tune a cold motor.
1. FIRST achieve a decent idle by screwing the idle screw in or out. If decent idle cannot be achieved by screwing the idle screw all the way in, adjust the air/fuel bleed circuit OUT to lean out the idle (max 3 turns). If idle still cannot be achieved, lean out the needle (metering rod) by screwing it out 1/2 turn at a time and start process over until satisfactory idle is achieved. If needle adjustment exceeds 2.075", double check everything, then contact your dealer: something is wrong! (in our experience, it is never necessary to exceed 2.050). This is not a cv carb. It should idle without dying, but it will idle a little rough and a little rich, but it shouldn't foul plugs. Set the idle higher than on your cv carb (approx 1800 rpm).
2. Next, tune for throttle snap. From approximately 3000 rpm, wick the throttle wide open. If you experience a bog, first try screwing in the air/fuel idle bleed. If this doesn't help, the needle is too lean and must be screwed in (do NOT exceed 1.969" on 46hv or 2.000 on 48hv or needle will lift out of body and stick wide open). If this setting is approached and it still won't take throttle snap, double check everything, then contact your dealer: something is wrong! You may need a different needle. Screwing the needle in or out will change the idle, and you must go back to step one to achieve idle again. Best performance is achieved when a puff of black smoke comes out the exhaust on the throttle snap. If throttle snap AND idle cannot be achieved simultaneously, double check everything, then contact your dealer: something is wrong! You may need a different needle.
3. Once idle and throttle snap are satisfactory, tune for top end. In an open area, run the atv at wide open throttle for several seconds. If the mixture seems rich or lean, change the power jet. If your not sure, always try a richer jet first. IF RICH: If the atv needs smaller than a #10 power jet, you may clamp or block of the power jet circuit- if this helps, you need a different needle. IF LEAN: If the atv needs larger than a #130 power jet, you may richen the needle 1/2 turn at a time, then readjust the idle. If the needle is richened to the point that idle cannot be achieved by adjustments, contact your dealer: you need a different needle for top end. If the top end is poor and changing power jets from one extreme to another does not seem to change anything, check fuel delivery to the float bowl, it may be running out of fuel on top end due to an obstruction or trash in the fuel tank, pet[censored], fuel line, or float needle seat. On dual power jet carbs, you may need a different float needle seat to supply the high fuel demands to the float bowl.