I don't know if it is patience or stubbornness. Crikey, I spent some time trying to figure out how these freaking carbs worked. In fact, One Man Band just sent me a Kart article on carbs that was pure BS - just typical of the crap out there you have to weed through. I'll post a link to the article and you can see what I mean.
If someone can come up with the schematics on the electronic carbs, I'll figure out some mods for those (I spent 7 years as an electronic technician and have modified electronic fuel injection systems).
I've been modding for 50 years now, its become a sick habit that I can't break.
EDIT: Here's the link to the Kart article, see if you can pick all the BS in it - it is chock full of it.
http://nkn.com/nationalkartnews/articles/AnatomyOfWalbro0708.pdf
I read through that article and find it wanting too. I'm curious what parts you didn't like, though I suspect I know. To me the biggest problem stems from his statement in Section C, pg 6:
For our purposes, it is enough to understand that the average pressures in the venturi are proportional to the square of the average intake air velocity (or, effectively, the square of the volume flow rate into the engine). In simple terms, average pressures in the venturi are typically less than atmospheric, and will decrease by a factor of four as the intake flow rate doubles. A complementary, and equally important, relationship governs the metered fuel flow rate. This is based on the same physical laws governing the venturi pressures above. The fuel flow rate is determined by the effective area in the metering circuit, and the square root of the pressure across that circuit. The effective area is the combination of all the restrictions in the flow path, like jet diameters, needle valve position, and cross sections in the flow passages. If the Walbro pressure regulator is doing its job, the pressure across the metering circuit will be held nearly equal to the pressure in the venturi (less the slightly negative pressure maintained in the metering cavity). Therefore, when the intake airflow rate doubles, the fuel flow rate doubles in step. This makes sense since the venturi pressure increases by a factor of four as the airflow rate doubles. The square root of four (relative change in the venturi pressure) is two, so the fuel flow rate doubles. Sounds complicated, but it isn’t if you pay close attention to what is being said here. The beauty of these physical relationships is that the resulting air-fuel ratio remains a constant. This is true despite wide variations in engine speed or throttle position.
This is incorrect, and does not match the known behavior of these carbs – we know that they provide a drastically richer mixture with just a small increase in air velocity (4-stroking), and most carbs in other application have air corrector jets to linearize the mixture.
I can see how he came to this conclusion. The Bernoulli equations show that the pressure at the outlet port is the square of the air velocity. But the characteristics of the flow of the incompressible liquid fuel through the jet is not the inverse of the compressible air through the venturi. This article (
http://en.wikipedia.org/wiki/Carburetor ) contains the following description:
The main disadvantage of basing a carburetor's operation on Bernoulli's Principle is that, being a fluid dynamic device, the pressure reduction in a venturi tends to be proportional to the square of the intake air speed. The fuel jets are much smaller and limited mainly by viscosity, so that the fuel flow tends to be proportional to the pressure difference. So jets sized for full power tend to starve the engine at lower speed and part throttle.
Later in the article he goes on to discuss how he didn't understand why some cart tuners were using the low speed circuit and deactivating the H circuit – it's because the L circuit on that carb actually has an air corrector jet and so can be made to meter correctly. They'd be better off adding an air corrector to the H circuit.
He discusses the L circuit air corrector jet, but misunderstands its function like many do. It is not to improve atomization, it is to turn the incompressible fluid in the jet into more of a compressible fluid, and then the flow is more linear with air velocity as he described.
Other than that, he seems a little foggy on the dynamic function (acceleration). The description of the main fuel diaphragm is decent for steady-state function.
