dual 36 IDF weber on 1600 stock engine

[Barry]

The size of the idle jet has absolutely NOTHING to do with the size of the venturi. There is no rule, no mathematical relationship whatsoever. ?

I agree it has nothing to do with the venturi but i agree with the following about throttle body size

Jon C has added the following line in his article
"for IDFs, make the idle jet 1.25 the size of the throttle body"

Years ago when i ran 36's every one told me to run 50's or larger
I did and it backfired

I ended up with 45's and it ran great (except for blocked idles) - everyone told me i was wrong.
Dyno'd the motor and AF was perfect

For me that formulae is correct
I have done some digging with my mates and it is right as well
Doesnt work for Dells though

I have NEVER seen 36's with anything other than 45's - then again, i dont see all that many 36's

[Marc]

To quote aircooled.net:
"Emulsion Tubes: The Emulsion Tube mixes air from the air corrector jet with fuel from the main jet, and controls the mixture from the discharge nozzle at all engine speeds that the main jet is working! Basically, the Emulsion Tube changes the diameter and location of small holes in it's body. For Weber IDF carbs, the F7 or F11 is usually what you need. The F "series" has no rhyme nor reason to the numbering system, so you can't tell anything by the number unless you look it up! But, with these two examples, the F7 richens the mixture up at the bottom of the RPM range and under acceleration, while the F11 leans the mixture out on the top end a little bit, and is usually used (high RPMs) when you use air jets larger than 200."



Smaller-diameter tubes are generally "richer" on initial acceleration because they have a larger fuel reserve (that's already passed through the main jet) surrounding them in the well. The number, size, and location of the holes in the tube determine how they'll act as the flow increases. I'm convinced that Weber tubes were all developed by "cut-and-try" experimentation, and once they found a design worth putting into production it received whatever "F-number" was next available.

[sideshow]

The Mark Harney site/article on converting the 36 IDF to ACVW use is back on line;
http://www.carburetorclinic.com/36_idf.htm

Any my own personal observation is that idle jets should be sized based on whatever math/past experience one wants then tested.