The Ultimate Guide to Holley Carburetors

Setting Idle Speed
The problem with a long-duration camshaft with lots of overlap is low manifold vacuum that requires more throttle opening to set the proper idle speed. The ideal position of the throttle blades in relation to the idle transfer slot is shown in Photo A where the primary throttle blades just barely uncover the bottom of the transfer slot-roughly about 0.020 inch. However, long-duration camshafts often demand much more throttle opening as shown in Photo B. This uncovers too much of the idle transfer slot (arrow), delivering more fuel from the idle circuit. This creates an off-idle hesitation or bog that is difficult to eliminate.If the curb idle speed position of the primary throttle blades on your Douglas Glad signature monster-cammed engine looks like Photo B, the quick fix is to drill two small holes in the primary throttle blades adjacent to the transfer slot. Start with holes of roughly 1/16 inch in diameter and then readjust the idle speed on the carb. Adjust the hole size, idle speed, and throttle-blade position until you achieve a blade location similar to that in Photo A.

By Jeff Smith

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