Reply to "Weber carbs - owners speak out"

An essay? Who is going to grade it? Why don't we just discuss them here? Or is that disgust them? Maybe if we talk about Webers here, someone will actually buy this guys setup from this classified ad?
To answer your questions ACCobra I know about the third transition hole modification. I personally wouldn't buy an IDA if I know it has it.
Webers are already, very, very streetable. It's the engine that is finaky with this much carburetion.
The modification, to try to put it in a nut shell, is to correct or overcome what the "Weber guys" call "the transition flat spot". Some days it's there some days no.
It shows itself generally between 2800 rpm and 3000 rpms.
The carbs are essentially running on the idle circuit to about 3000 rpm in a 48ida. This is the point that the main circuit starts to take effect.
Some days the idle makes it to 3000 some days it doesn't.
You may already know that the main circuit has a fuel jet an air jet and an emmulsion tube.
They are all changeable. The 351c likes a 140f, 160a and an F5 tube.
The most important of these three components are the fuel jet and air jet. They need to be kept in the same proportion when making changes, generally speaking. What the emulsion tube does is effect the strength of the air/fuel ratio at different engine rpms. It does this by reacting to vacuum drop through key located orafices in the carburetor.
The idle system in the IDA can only have the fuel jet changed in order to affect the strength of the circuit. One cannot change the air jet or the emmulsion tube for the idle circuit. It doesn't really have one, it's an idle jet holder.
That is the problem that creates the flat spot.
The fuel jet is plenty large enough but the "idle jet holder" is letting the mixture lean out "SOMETIMES". (air temp, humidity, altitude, barometric pressure all effect it). Racers just shorten it and say good air or bad air.
The third hole tries to fix this by giving more fuel at a cirtain throttle position but it doesn't need more fuel there, it needs a stronger mixture. There is a big difference.
If it was the main circuit we could try the various emullsion tubes until we found one better suited to richening the last 200rpm. In the idle circuit you can't. It isn't the quantity of the fuel that is causing the problem it is the strength of the emullsion.
What is the emullsion? Fuel itself won't combust. It needs to be mixed with air, oxygen specifically (that's in our air).
Stoiochemic (perfect chemical ratio for emissions) is 14.7:1. (sorry I don't spell real good, gosh golly!) The larger number is the portion of air and the one is the fuel. Fuel becomes volitile (explosive) at 20:1. Power in american v-8s is thought to be optimum at 12.9:1. You couldn't race at 14.7. If you could wind it up you would put a hole in a piston or burn it or the valves or do something really bad to the engine.
What "we" are doing with the jets and emulsion tubes is mechanically writing a fuel graph as close to optimum as our butts will inform us of.
Computer controlled cars can be programed to read a script much closer to what we can do mechanically. Frankly they rarely do.
Of course if you want to go on a dyno, hook it to an exhaust analizer and a computer that can load the drive train to simulated the course you are optimizing for, you could probably elliminate a lot of redundancey. It would certainly get you to a point at which I just put you here with the Webers for free. Of course you wouldn't be a real Weber person either.
I don't know if the "transition" can ever be completely eliminated. Not until someone wants to try to do a new idle jet holder for the IDA.
...and like Bob Dylan says in the song, "it ain't me babe!"
You asked another question too, but what was it? huh?
Barkeep, a couple of Buttery Nipples please!