Senior Tech Team
Join Date: Apr 2012
Location: Yerington, Nevada
Re: Air/Fuel Mixture
FIRST to check is the idle throttle plate settings. Holley has what are called Idle Transfer Slots in their throttle bores. These slots hold fuel in suspension when the plates are sitting in the right places at idle, and discharge that fuel when the plates are opened. This fuel is first into the manifold off idle, NOT accelerator or other circuits.
The primary throttle plates should be set to allow only .020 opening of the ITS at their hot idle setting. Too far open, engine will use that fuel to idle, and there will be an off idle hesitation.
I set it up so I can see where the throttle plates are down the throttle bores, instead of having to pull the carb to see them, easy to do. With the carb off the engine, set the idle setting to have the ITS open .020, then, mark a line across the throttle bores ABOVE the plates, so yu can see the line down the bore, put the carb back on and go forward.
If the ignition system is set up correctly, and the carb is working correctly, idle should be stable at the correct throttle plate setting.
If the engine insists on having too much open throttle to idle, it indicates the engine wants more air to idle correctly. This usually is needed for bigger cams in engines. Holley counteracted this by adding bypass holes in the throttle plates, but, do not just go off drilling the plates, the holes and sizes are critical, and the very last resort in getting it right.
Check the ITS first.