NoShortcuts (9/19/2011)

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ENGINE TUNING: Valve lash should be properly set. Adjusting the carb. idle mixture is done after spark plug gaps have been set, distributor point dwell angle adjusted, and the initial ignition timing has been adjusted or checked for correctness.

Initial engine timing is adjusted and set with the vacuum advance line between the dual quad rear 'E' carb. and the distributor disconnected and closed-off with electrical tape. It is critical to set initial ignition timing with the engine at its proper engine idle rpm.

IF you have trouble getting the idle speed as low as it should be, check for vacuum leaks. I'm told that high engine idle speed with the 'E's is not uncommon. Sometimes, the high idle on the 'E's is attributable to worn throttle shafts of the Holley 4000s. OUCH!

I adjust the idle mixture screws on a carburetor with the engine at normal operating temperature using a tachometer or a vacuum gauge. I prefer the tachometer, it seems more telling of the screw adjustment. NOTE: This adjusting of idle mixture screws can take some time. Consider putting a box fan blowing air into your radiator opening to insure keeping the engine operating temperature 'normal'.

In addition to the engine being at normal operating temperature, the engine idle speed must be correct before beginning idle mixture adjustments. Check the engine idle speed with a tachometer.

For an auto. transmission car, block the wheels, put on the emergency brake, and put the car in gear to attain proper idle speed. [Alternative method... safer!.. leave the car in Park, reduce the idle rpm using the throttle adjusting screws on the two carbs. Don't forget to readjust the 'in drive gear' idle speed when you are done.]

If using a tach., adjust one idle mixture screw at a time on one carburetor adjusting for maximum r.p.m. reading.
- Turn the idle mixture screw approx. an 1/8 turn at a time and watch the rpm reading. Adjust it clockwise or counter-clockwise until you get maximum idle speed.
- Take some time doing this, it takes a little time for adjustments to be accurately reflected in the tach. reading.
- Go back-and-forth between the two adjusting screws on the one carburetor to insure that adjusting of one hasn't affected the adjustment of the other.
- Remember after you've adjusted a screw on that first carburetor to readjust the idle speed to its proper level if it has gone up.

With the dual quad set-up, you've got four idle screws to adjust one at a time. Do one carburetor at a time, adjusting the two idle mixtures screws on the one carburetor first, then do the second carburetor and its two idle mixture screws.

After you've done both carburetors, i.e. when you're done adjusting the two screws on each, recheck your settings by going through the whole thing again starting with the first carburetor that you adjusted.
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If using a vacuum gauge, again adjust one idle mixture screw at a time adjusting for maximum vacuum reading. Turn the idle mixture screw approx. an 1/8 turn at a time and watch the vacuum reading. Take some time doing this, it takes a little time for adjustments to be accurately reflected in the vacuum gauge reading. Go back-and-forth between the two adjusting screws to insure that adjusting one hasn't affected the other.

The rest of the adjusting process is the same as what was related above when using the tachometer as your idle indicator
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Already stated above, but remember to check and adjust the engine idle rpm as called for as you do the idle mixture screw adjustments. Adjusting the idle mixture screws (especially if they are significantly out of adjustment) should significantly affect engine idle speed if your carburetors are properly rebuilt.

When all done adjusting the idle mixture screws, remember to reconnect the vacuum line between your rear 'E' carb. and the distributor.
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If you're in need of specific settings for plug gaps, point dwell, initial timing, for your 'E' application, let us know.