The Lectron Thread

osteoderm

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Tons of carbs available to fit these bikes; Keihin, Mikuni (BS, VM, and I think there's a few folks on this thread running TM's), Dell'Orto, and Lectron. There's probably others, but this thread is for the Lectron folks. Likewise, I hope this thread won't descend into an endless pro/con debate over these carbs. They're not for every rider, every build, or every budget, but for those of us running them, or those of you who would like to try, I hope this thread can become a resource to refer to.

Loads of decent BS and VM tuning advice on this forum, but the Lectron info feels pretty thin. Just this thread and this thread and this thread here that I've found. Hugh talks about his Lectron setup in this interview. Also some interesting commentary here.

I'm not going explain the Lectron carb right here in this thread. If you haven't already, read this page and this page first.

The basic set-up for the XS650 seems to be Lectron 34mm carbs, long Shell-style intake runners, single adjustable powerjets, and nonrestrictive filtration (ie., large foam UNI's, not short K&N knockoffs). The only real variables are metering rod choice and rod tuning.

Hugh Owings (who I hope will join this thread) has variously described using FBG-1XL rods, 0-1XL rods, and 0-2XL rods (on his bumped-compression 707cc rephase). Kevin from Lectron recommended 0-2XL rods for my own bike (fairly stock, details to follow).

There's an almost infinite number of metering rod grinds, but since each one covers a range of approximately 10 conventional main jets in a Mikuni, in theory you only have to get in the ballpark to get started. Without a bunch of dyno work or other controlled testing, every other rod choice is conjecture.

As for tuning, there's a couple numbers floating around the interwebs. The current Lectron tuning guide, straight off their website, suggests setting the metering rod length at 2.040", as measured from the bottom of the threaded brass rod insert to the tip of the metering rod. Note that this is only a suggested starting point for 4-stroke applications!

Lectron sells a Fuel Ratio Tool which allows for much greater accuracy in setting the correct starting metering rod height, and despite the expense, it seems like a simple way to avoid a ton of fiddling and frustration if you plan to change rods or reset to a baseline often.

If you're running or have run these carbs, please share your tuning, along with general engine build/mods that might apply. Also please leave your general impressions, experiences, and suggestions for what has and has not worked out for you!
 
Careful tuning of any bike isn't as simple as copying somebody else's settings. Every bike, even those outwardly identical, will be a little different. However, I've found it useful to know what other people are running for tune, and how their bikes are built, even when it's different from my own. Recording and comparing careful observations builds a useful reference for us all.

Here's my engine and tune, in a snapshot:

'74 XS650, assumed stock engine internals, stock engine displacement
Gordon Scott 2-1 pipe (1-1/2" primaries, 1-3/4" secondary, straight-through muffler)
PAMCO ignition; "Ultimate" coil, electronic advance, iridium plugs
Hugh's PMA
TC Bros intakes with 1/8" vacuum barbs tapped in, close-coupled to carbs with 2-1/8" hose cuffs
Full 5/16" fuel system, ie., petcocks, inline filters, hose.
5" foam UNI's, no oil

Lectron 34mm carbs (assumed standard "low velocity"), adjustable powerjets cracked open 1/8 turn
0-2XL metering rods, set to baseline with Lectron Fuel Ratio Tool, then progressively adjusted 1-1/2 turns leaner until plugs (mostly) stopped fouling. Still tuning!

Carb sync set using combination of vacuum guages on intakes and temperature readings off of header pipes.

Observations, with regards to my previously-installed Mikuni VM34's:

Bike starts first kick, hot or cold, no choke every time. My VM's needed a little choke and a few kicks when cold.

Immediate throttle response. "Snapping" the throttle open with the VM's would cause a bog and stutter, but the Lectrons just GO. Overall seat-of-the-pants power increase. Very slight part-throttle lower-midrange (2500-3250rpm) torque loss, but higher rpm and/or larger throttle openings just blast through that. Engine pulls full-throttle just as hard at 80mph as it does at 50mph, with no obvious fall-off through 90mph; I have yet to discover the point where the bike runs out of breath.

Bike will not practicaly idle below 1500rpm. Engine "loads up" in city driving; must be blipped above 2250rpm nearly constantly to avoid stalls in traffic. Sitting in the driveway, I can coax the idle down to 1200, where the engine starts cycling itself through a 500rpm-range; I'm guessing this is either/or sync or richness.
VM's could be lugged along at 800rpm, feathering the clutch a little in traffic. Now, dropping down to 1000rpm, even while in gear, almost guarantees a stall.

Bikes pops and cackles on overrun/decceleration when throttle is held barely cracked. 1/8 throttle stutters on acceleration, and steady-speed cruising at any rpm with under 1/4 throttle results in surges and revs "hanging" when the slide is released. These all point to a lean condition, but the plugs, exhaust note/smell, and carbon on the piston all say rich.

Off-idle low/mid-rpm riding with the VM's was very nice; the Lectrons are jerky and annoying, more of an on/off switch. However, once above 1/4 throttle or 3500rpm, the engine is completely and powerfully transformed.
 
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"High Velocity" Lectron carbs are also available; these are not neccesarily better, just suited for different applications, ie., engines with low "port speed". As far as I know, that describes the XS intakes, but different styles and amounts of head porting/polishing/reshaping could have huge effects.

Hugh has been advocating these, and had I bought new, I would probably gone for the High Velocity option (they cost the same, I believe).
 
I know there's some sort of quick-release clip arrangement available for the carb tops, and while I've seen pics, I haven't found any for sale. Lectron does not offer these directly.

After dropping the stubbiest screwdriver I own more times than I care to relate, I found another solution to quick'n'easy carb top removal:

2013-06-01 16.12.33.jpg


The tall knurled stainless 6-32 screws are from McMaster-Carr, part #91746A848. The threads are just a teeny bit long, but with #6 SS lockwashers under them, everything fits great, and tool-free access to the metering rods is made much simpler.
 
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Me too . Been waiting for someone to post some info on Lectrons . So, how much power did you gain on a stock motor with them ? I don't mean dyno numbers , just how does your bike feel now ?

Major and immediate. On the same stretch of road where I might hit 80 before running out of road and/or balls and brake for the bend, last hit 89. The bike was fun before, but is now slightly scary. Which is okay.
 
Sweet ! I am getting my bike dialed in nicely . Mine is stock as well (about 25000 K on it ), just did a compression test and got 148 and 150 , but will check again after I get the carbon blown out ( bike sat for a while ) . I like bolt on performance parts. Instant gratification !
 
I like bolt on performance parts. Instant gratification!

The benefits of high-performance carbs such as these are only realized when installed in concert with upgraded exhaust, intake, and ignition. Also required are changes to throttle cabling and fuel lines. Of course, much post-installation tuning is also required. While the overall gains are clear, this is not an example of "bolt on performance". Careful research, preparation, and patience are key.
 
Have you checked for vacuum leaks? Just curious...

Fair question. Vacuum gauges consistent, strong, and steady both sides. Unlit propane torch played over manifolds and carb bodies does not raise rpm significantly. Activating "choke" bogs engine; pulling vacuum barb cap while running causes engine to race lean.

Further fine-tuning of slide-lift sync and another 1/4-turn leaner on the rods has yielded stable 1400rpm idle, but off-idle stuttering still apparent. Plugs approaching acceptable color.

I'm getting the feeling that this carb/engine/rod combo is very sensitive to cable sync; an 1/8 turn of cable adjustment on one carb has significantly diminished vibration off-throttle through 2000rpm.

Above 1/4 throttle at 3000rpm+, bike remains a beast. After these last few days, I'm learning to adjust my riding style to accept the fuel loading and crankiness in traffic around town; they are vintage drag-bike carbs after all! Re-installing the VM's becoming an increasingly distant option.
 
any idea how old your carbs are?heard the newer ones have changed a little bit from a few years back??? dont know if thats true or just hear say.
 
any idea how old your carbs are?heard the newer ones have changed a little bit from a few years back??? dont know if thats true or just hear say.

I hope so... this thread is sort of disappointing. Not what hugh has previously described in his experiences with lectrons, and more in line with the myth that lectrons are race only carbs.
 
any idea how old your carbs are?heard the newer ones have changed a little bit from a few years back??? dont know if thats true or just hear say.

The Lectrons have changed over time, according to their website. My carbs have all the hallmarks of being vintage ex-alcohol units. I think the biggest changes have been in quality control and metering rod accuracy/consistency.
 
Not what hugh has previously described in his experiences with lectrons, and more in line with the myth that lectrons are race only carbs.

My experiences may not be typical; I'm hoping other folks running these carbs will chime in with their own observations and experience. I'm not sure that there's many folks running these on stock-displacement motors, but but I'd like to hear otherwise!

I still feel like I'm in the early stages of tuning these carbs for my application, and that improvements will keep coming. I've only put on about 200 miles with these carbs, constantly fiddling and taking notes. Getting my VM's running smoothly and consistently took me way more miles than that.

I can already tell that the "race only" myth is just that, but I can see why people fall for it. They certainly are a high-performance piece of kit, and while streetable, there are certain compromises.
 
Another 1/4 turn leaner on the rod (what is that, two full turns now?), more careful careful slide height and lift syncing, and I'm getting somewhere. Plugs no longer fouling, stable idle at 1200rpm, off-idle stutter gone. A little bit of accelerative grunt lost below 3500rpm, but still impressive.

Pulling a vacuum barb plug now causes a ragged rather than racing idle, so I'm comfortable in thinking that my tune is close to being as lean as practically available with these rods. Time to start playing with the powerjets... :thumbsup:
 
how is your traffic use now? are you still stalling in traffic.should be intresting with the power jets alterations.keep up the good work.
 
I have been watching this thread I have a small collection of older (smaller 30mm?) NOS Lectrons but none on a bike so far. I also heard that QC on the metering rods was so so at best.
IMHO It's a simple carb and that means in some respects it will be crude. Mikuni etal didn't make em' complicated just for the hell of it.
 
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