Weber idle adjustment

Superfly · #1 (**permalink**) 01-06-2005, 01:00 PM

After many failed attempts to adjust the idle mixture on my Weber 40 DCOEs I decided to cheat and bought a ColourTune. On every cylinder the flame color is yellow until I turn all 4 idle adjustments in all the way (almost seated). Even with the adjustment all the way in the flame color is just barely turning blue. I should mention that these carbs were originally on a 1600 and now are on a 1750. I changed the jets to the specifications for an ALFA 1750 per the Weber manual.

The current jet sizes are:

Main 1-30

Idle 50-F8

EmTubes F9

Air Corrector 2.00

Is there something else I should be looking for or should I re-think the jets I installed?

Scott
67 Giulia Super

Mr. C. · #2 (**permalink**) 01-06-2005, 02:43 PM

Hi Scott,
What size Venturi's are in the Webers? You should be running 32s but the 1600 probably had 30s. I am not sure that the difference is enough to cause the problem but you are not getting enough air or too much gas.

**papajam** · #3 (**permalink**) 01-07-2005, 07:46 PM

The jetting sounds good to me. I've never used a colortune but I'll assume a yellow flame is too rich? If so, the first thing I'd do is check base ignition timing. If it's too far retarded, the base idle screw will be turned up in order to bring the idle up to specs. This could open the throttles enough to uncover the first progression holes and enrichen the mixture resulting in the mixture screws needing to be closed (or almost closed) to lean it back out for a decent idle. 2-4 deg BTDC should get you in the ballpark.
Second thing is the float level; it could be too high.
Third. Idle screws and/or seats damaged from overtightening.
Forth. Carbon buildup around the butterflies.

**blu58spider** · #4 (**permalink**) 01-08-2005, 10:32 AM

I'd bet its the timing, per Papajam's suggestion because it's affecting all four cylinders.

But if its some other problem I'd add that along with float level you should check for leaky floats. If you can hear gas sloshing in the floats themselves, they need replacing. You can't check that without taking the carbs apart, but when my SS had this problem it was dripping gas from the carbs at idle because the floats were sunk.