Where do DCOE idle Jets F17 - F27 fit in the rich-lean scale?

[andrewzuku]

Hey all (especially engineers and carb gurus),

I've been able to find the dimensions of all the DCOE idle jets, but can't come up with a formula to sort them in the same order as the Weber literature:

Early type:	Rich - F6, F12, F9, F8, F11, F13, F2, F4, F5, F7, F1, F3 - Lean
Late type (for 151 and 152) ?:	Rich - F19, F23, F25, F24, F27, F26, F17, F18, F21, F22 - Lean

Download as an Excel file: Idle Jets for DCOE.xlsx (122 KB)



I tried sorting each type by the sum of the air hole areas ('C' on the diagram), but the results are slightly different to what's in the "Haynes - Weber Carburettors - Owners Workshop Manual" I have.

Obviously that approach is a bit simplistic, because it ignores dimensions 'A' and 'B'. Does anyone out there understand air/fuel mixtures at a "first principles" level well enough to help me sort these into one big list?

Are F17 - F27 strictly only meant for the newer 151 and 152 DCOE carbs?

Ultimately I'd like a complete list from F1 to F27 sorted from rich to lean.

[ae92gtapex]

Check out www.weberperformance.com.au .. Has a bit of info on stuff there. This is interesting:

"DCOE Weber carburettors have an air bleed hole drilled into the idle jet (noted as an "F" number). They help emulsify the mixture prior to fuel entering the engine. There is no correlation between "F" numbers and their action - they are randomly assigned. Larger holes in the idle jet will allow more air therefore weakening the mixture"

Cheers,

Gaz

[andrewzuku]

Thanks for the link Gaz, I'll be buying a few jets from them soon They make excellent YouTube how-to videos too.

As far as I understand, the F numbers are in chronological order. Meaning F1 was designed before F2 and so on. But that's all you can tell from the F number.

I'm hoping that, given the chart of measurements above, it's possible to calculate their air/fuel mixture ratio for each. Then I could sort them by that value.

[Dazza]

The F1 to F16 jets have a different outer profile to the F17 to F27 jets. F17 to F27 jets are used on carbies with the idle jets screwed into the sides which have a separate air corrector jet. F1 to F16 jets are used on carbies where the idle jet screws in from the top under the jet cover and does not have a separate air corrector jet. Air correction is done with dimension C on the diagram that you show

[andrewzuku]

Excellent. That settles it then

I have 55F17's in my 45 DCOE 13's (early type without an air corrector screw). So F17 - F27 for me are a no-no ?

[Dazza]

I would think that F17 jets would make it run lean.