I started a new thread with this information to make it a little easier to search for it specifically. This information is from Corey (VP of Development at APT).
"The Lectron and the SmartCarb are each a very fine example stemming from the original Edmonston designed single circuit flat slide carburetor. The distinctions however between the Lectron and the SmartCarb span nearly 45 years of development with no less than five other varieties in between. These less known iterations include the EI Blue Magnum, the Daytona Quicksilver I and Quicksilver II's, Edelbrock Quicksilver, AFT and finally theSmartCarb.
William H. "Red" Edmonston and I were partners at the time of his passing and most of the development work for the SmartCarb took place at the University of Wyoming in our 2 stroke research and development laboratories. Red clearly understood the limitations of a single circuit system and the fundamental flaw imposed by a more or less round throat venturi. The trough or valley at the bottom of an Edmonston designed venturi was quite well understood by this time and it can be found on a Lectron. It is this feature that led to what was really the beginning of our understanding the importance of concentrating and accelerating as much of the actual airflow through the venturi, right at the base of the metering rod and nozzle interface as possible, at all throttle positions. In a more or less round venturi, the rate of throttle opening from idle to half open is exponentially divergent, meaning it’s getting much larger, faster, the farther you open it. From half to wide open, however, the lines of the circle are converging and the rate of opening is slowing even though you are now almost wide open. This causes the pressures through the venturi to swing wildly as you move the throttle slide bottom to top and vice versa, which in turn causes the signal to the metering rod to fluctuate, and unless corrections are made by altering the angle of the metering rod crisp throttling and consistent fueling suffers.
(Signal referred to here is the negative value created by the piston displacing air as the engine cycles, creating a pressure drop within the venturi as air rushes in, thus allowing atmosphere to push fuel up through the nozzle, past the surface of the metering rod and into the intake airstream. In the case of a metering rod carburetor this signal is also read by the flat of the metering rod which creates another secondary low pressure zone.)
The difficulty of putting very accurate changes in angle along a 1/8” surface of a metering rod is maddening and is Lectron’s biggest challenge. This is one reason Lectrons are most noted as a drag racing carburetor and was a place they were found to work really well. Today I do believe they have made tremendous progress in metering rod development and the addition of a power-jet has made their job a little easier. IF all the angles are correct, for the right engine, and the PJ is set correctly they work really well through the whole range much better than a conventional carburetor.
Red felt the better solution was to shape the venturi as such that we could maintain an even pressure against the metering rod through the whole range of throttling. The question was how to do that without giving up a lot of flow and limit the carb’s full potential size for size. He understood laminar flow very well and we did a lot of experimenting with lead in curves to control airflow and get the carburetor to gulp a lot of air, even though the neck of the venturi was unconventionally restrictive. We also added a nose to the slide to further direct and compress airflow leading into the metering rod. What really tipped the scales technology wise though is the ambient air density correction circuit and how it interrelates to the venturi. Most people understand this to be the altitude correction circuit, which it is, but it is really much more. It provides an instantaneous dynamic balance between the pressures the throat of the carburetor is actually seeing and the ambient air pressure against the top of the fuel in the float bowl in all conditions. Perhaps a more familiar term people recognize for this effect is Manifold Absolute Pressure and is something that all modern closed loop EFI systems rely on for correcting air/fuel ratios with changes in ambient air density. Apart from the venturi shape this feature alone is what allows the SmartCarb to only need a single angle grind metering rod, and in most cases a common grind across a very large variety of products and applications. This circuit also acts much like a power jet at the very top end when the static pressure being applied to the fuel in the float bowl also becomes dynamic and liquid flow lift ensues, hammering fuel up the nozzle directly proportional to total flow through the venturi. This is actually much superior to a power jet in that it remains finely atomized, because it is after all still using the main (and only) circuit, whereas a power-jet is literally throwing fuel on the fire and is emitted as almost pure liquid when it enters high into the air stream. This isn’t the worst thing, however it does dramatically affect Lectron’s full potential for fuel economy gains, altitude compensation and emissions reductions and it effectively makes it yet another multi circuit carburetor.
The drawback to the SmartCarb air density correction circuit is lack of a float bowl overflow and the necessity of tip over valves, along with the additional problems they create. The performance benefits the system offers are more than worth the effort though and the tip over valves, along with additional functionality to further protect our patents for the scoop and venting system, offer a very desirable side benefit in that now the carburetori s completely sealed. Certification testing shows the SC to be the lowest evaporative emissions carburetors ever test. Plus there is no raw fuel spillage on the ground and it fits very conveniently into the new epa tip over ruling for motorcycles. Who’d of known they were about to implement that? We are continuing to improve the system and are implementing changes to eliminate sticking issues.
With all of that said, I have just one more thing. Make no mistake, Lectron is not our competition. Our competition is all modern fuel systems worldwide, electronic or mechanical. Here’s why; any emissions reduction strategy requires a fuel system that is able to two things very well. Finely atomize fuel and maintain extremely accurate air/fuel ratios. TheSmartCarb simply does those two things better than anything else we currently know of period, and it does it without electronics. For instance we are in the second leg of EPA Tier II and ARB on road emissions certification for Zaeta’s TM powered 530 DT motorcycle (google it). This is TM’s open enduro race 4t engine they have attempted to prior certify in North America themselves. They have tried twice , both times using two precious metal catalysts and a race TMXX Mikuni downdraft, both times unsuccessful. APT is actually touching on Euro III numbers with this bike and is passing EPA and ARB easily with just our new 40mm side pull FCR replacement carburetor and no cats. In fact we are under Tier II CO emissions by nearly 90% and HC and Nox 38% and 16% respectively all this with a 28% gain in fuel economy. This is no joke and these aren’t the types of things you are hearing about in the forums and possibly in a lot of people’s minds on a performance related forum this may not seem like a big deal at all. But actually it is everything. "
