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Discussion Starter #1
1600 motor w/DCOE 2 carbs, 33 mm venturis. After moving to 3000 feet from sea level, car runs rich. With idle screws out only a little over half-turn, plugs still get black. Also, the motor starts and runs suspiciously well even when it's very cold (I have never used or even connected the cold-start devices). It starts very well, and pulls strongly from 2500 RPM onward, but when I get back on the pedal after shifting, there's a brief hesitation that sounds like some race motors. 50 F8 intermediate jets are installed. What would be the next leaner jet?

Thanks!
 

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Richard Jemison
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Jets

For the size of your cylinder volumn you should have 40 F8 idle jets. If they are still rich, you can drill the air bleed hole larger to make them 40 F11s.
You will likely have to reduce the main jet size as well.
 

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Discussion Starter #3
Thanks much. I've never understood what the numbers mean. I guessed (right or wrong?) that the 50 means "0.50 mm" but the F number remains a mystery. I have some 60 F5 jets on hand that were in the carbs originally (they're marked EW) that have an air hole much larger than the F8 jets, and then I have some jets marked just 40 with no effing F number at all, in which the air hole is smaller than the F8s.

Those are some really tiny drills. Any idea what size hole would make the F11?
 

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Those are some really tiny drills. Any idea what size hole would make the F11?
The fuel hole and the air hole in 50F8 and 50F11 idle jets are the same size - 0.5mm and 1.2mm respectively. The internal bores are different. F8 is 2.00mm and F11 is 1.50mm. Opening up the air hole to 1.4mm would turn an F8 into an F4. The order of idle jet suffixes from rich to lean is: F6, F12, F9, F8, F11, F13, F2, F4, F5, F7, F1, F3. It is possible that someone knows the logic behind this sequence!
It would be easier to turn an F8 into an F13. Fill up the air hole with solder and drill two new holes of 0.9mm, 180 degrees apart.

You could make a 40F8 by filling the fuel orifice with solder and then drilling it with a 0.4mm drill.

I bought some type b idle jets (for emissions Webers) from an ebay seller in Italy last year and they did not conform to the Weber drawings. I modified them to make them correct. I ordered some 50F8's from an ebay seller in the Czech Republic today. It will be interesting to see if they are correct.
 
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