Interesting Weber jetting

[Eljaro]

Brent,
my last drive during a rally was with this setup on the 48 IDAs:

Main venturi 40mm
Third progression hole drilled (might not be necessary)
Idler jet 65
Idle screw 1 turn out (3/4 turn only would produce too much exhaust popping)
Idle holder 100 ( the 60 holder was too rich at cruising speeds at 2000 rpm )
Main jet 150 ( with smaller jet it would lean out at WOT in 4th gear at 6000rpm)
Air Corrector 120 (larger air correctors would lean out the mixture too much at WOT)
Emulsion tube very similar to F14.
Its actually a F7 modified tube with no holes in the bottom part but only at the top. So you get aireation during the low transition (holes on top), thus leaning out there, and no holes at the bottom, which produces less aireation at the high transition band, thus richening the mixture until the main jet takes over from there.

Pump bypass 00 (would bog down with a .50 when stepping on the gas suddenly).

The car ran fantastic with this. Maybe I should try a .35 pump bypass because the sidepipes were showing black smoke when accelerating.

Finally I think I have understood how the webers work. Testing the car after every minor change and writing the result and the reading from the lambda sensor down showed some patterns. All the changes I made overlap to some degree, so I had to try all the different combinations.

Basically the changes going up the rpm scale are influenced in this order:
idle jet - idle air corrector - emulsion tube outer and inner diameter - holes on top - holes at the bottom - main jet - main air corrector , while the emulsion tube and main jet overlap in its influence and are the ones affecting the transition the most.
The light tan color of the spark plugs confirms that the mixture is now almost perfect.

But all this was only possible after I changed the main venturi to 40mm inner diameter.
With the 37mm chokes things never worked right, and the plugs were allways black, which means too rich mixture all over.
What the 37mm choke/F5-F7 emus.tube/60 air corr./ setup was doing is overly richening the transition over a broad band to go over the stumble.You are effectively pouring gasoline all over to get one spot right.

And here is a hint from Inglese in their technical primer: (giving away some crucial information btw)
Pull out those small chokes, drop in some large-diameter ones, which may be nothing more than thin-wall "sleeves", and you've got a set of 48 IDA's that will flow enough CFM to make a big block scream.

All said.
Stefan