Tech: Lectron Carbs by Dale Alexander
Hi all! Been reading the current string about Lectron carbs and would like to fill out some info.
Over 20 years ago, I remember having a set of Lake "Fuel Injector" carbs on my Norton Commando 750. I believe this to be the precursors to the Lectron style carbs. The Lake carbs did not have a float system at all, just a fuel line to the bottom of the carb where the needle would be. I don't remember how the mixture was adjusted as I never did adjust it! Hey! I was only 16 at the time and not old and smart(assed) like I am now. The carbs didn't qualify for more than a calibrated piss as far as accuracy but as they were one of the first "smooth bore" designs out there, they flowed a lot of air so power went up, even if it was crude power at best. And they looked cool. Exotic. Had to work better if you know what I mean ; )
Posa carbs were a like design so I won't spend any time on them.
Lectron carbs were much the same as well but with two VERY important improvements: a float system ala Mikuni and a powerjet top end fuel supplement.
Nothing special about the float system. It was a natural progression to correct what Lectron saw was a weakness in the Lake type carb. It allowed precision in the float level. The Lake was prone to flooding and hard starting(duh!). The power valve was a new concept at the time and Lectron was the first carb I remember seeing with a power jet and should be note-worthy in that fact.
HOW LECTRONS WORK
The Lectrons have a central fuel outlet, that being the needle area. The needles controlled all fuel now with the exception of the power jet. One of the ideas was to eliminate the rich and lean spots in the fuel delivery curve as can happen with a multi-area delivery device such as a normal carb. The other was to make a system that was easy to adjust. Lectron succeeded brilliantly in one area, failed miserably in the other.
Fuel control was with the needle. A taper was ground into the needle on the side that faces the intake area of the engine. Needles were graded and marked 5-3, 6-1, 6-2 etc. These numbers were easy to understand. The first number was the overall richness of the needle. A 5 series was leaner than a 6 series. The second number was the top end richness. A -3 was richer than a -I. The very top end was controlled by the power jet exactly as we understand power jet function now.
In order to have a "base" point that tuning could be initially set to, a distance was specified as standard, a datum. This was the length of the needle from the adjusting nut(what would be the needle clip in a Mikuni) and the tip of the needle that extends into what would be the needle jet in a Mik. The "needle jet" was not adjustable, much like the TMX style of Mik. The standard length was 1.945" or something like that. If the length was longer, the overall fuel was leaner as the taper would be lower and this would allow less fuel for any given throttle opening. The opposite was true if the needle length were shorter than 1.945". I think that if you had to go more than 2 turns in either direction, it was time to change the needle for a different fuel curve. This allowed for the fine adjustment of fuel.
If one were to replace the screws holding the top of the Lectron with snap clips to allow quick removal of the top, a minor needle adjustment with power jet swap could be made in about 2 minutes for 2 carbs. This was one of the Lectrons strong points.
If jetting was ok in the mid-range but off a bit just before power jet came on, you wouldn't want to adjust the needle as this would upset the balance with the mid-range. You would select a needle with a different second number - 1, -3 etc. THIS is where the Lectron failed. The quality control of the grinding of the needles was such that even though you had two needles marked the same, it didn't mean that you hade two needles that were the same. At first this caused all kinds of confusion as one would change the needles expecting a change in a known area and the engine wouldn't run anything like what was expected. Only after measuring the needles very accurately at absurdly small stations were we able to ferret out that Lectron needles were ground by the firm of "Byguess and Bygolly"!
The only way to solve this problem was to carefully hone stone the needles and hope that the results gave you a pair of needles that could be used together, run them, grade them, and hope that one was fortunate enough to get a selection after a while. With all this tuning work done to the needles, it's not hard to see that if one had a good set, they didn't get loaned out at all(Hey! I need as set of 6-2's. Got any I could borrow for this race?) Might as well part with your right arm once your friend figures out your needles work better than his!
On of the other strong points was that without a pilot circuit, the Lectrons could be run at absurd angles(35 deg) compaired to the Mik's. This allowed the carbs to be mounted to a straight manifold on the Super-street RD's for a more direct shot at the intake. If a Mikuni was mounted this way, it would flood horribly under hard braking as fuel poured out of the pilot circuit. This was not a problem with the central fuel point on the Lectron's.
But time moves on and the quality control finally caught up to Lectron(and some other problem with finances or something). Carb technology advanced as well and we have very good, though expensive stuff now that needs computers to do all the thinking where us mortal humans did it before. This is progress...I think.