Carburetor Idle Problems

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When a car problem occurs, the first step is to trouble shoot the related system. Then, perform simple tests that can lead you to the cause of the malfunction and the repairs needed to correct the problem. Follow the "first thing to check" list and test by symptoms how to test for a problem, then execute the proper repair.

To repair Holley carburetors, Granger recommends using either a Holley rebuild kit and gaskets or a quality aftermarket kit. Inferior gaskets can cause driveability problems or fuel and vacuum leaks. It's also important to use the proper tools. Flare wrenches, correct-size screwdrivers, and a clean work space all contribute to a quality rebuild.

Is your carburetor giving you idle problems?

If so, start with the basics. For most Holley carburetors, the air/fuel mixture screws should first be set to 1-1/2 turns outward before their final adjustment. Always adjust all idle mixture screws evenly.
To allow your distributor's vacuum-advance unit to operate properly, the hose should connect to a ported vacuum source and not direct vacuum. A good test for this is to remove the plug with the engine idling and check for vacuum. There should be none at idle.
When wiring the electric choke on a Holley carburetor, run a 12-volt source from a switched terminal. Never connect the choke to the positive side of the coil.
An air cleaner not only delivers clean, undisturbed air but also minimizes the chance of a fire spreading in your engine compartment. Also make sure that the air-cleaner lid does not block or interfere with the carburetor vents. If this happens, stalling can occur.
After installing the carburetor, check wide-open throttle (WOT) operation. For proper throttle return, install a return spring that is just strong enough to pull the throttle back. Too strong a return spring can cause unnecessary wear to the throttle shaft and bushings.
To remove a stubborn fuel bowl, tap it with a plastic mallet. Using a screwdriver to wedge the bowl away from the carburetor body could create a permanent leak.
Be careful during reassembly because over-tightening the carburetor can strip threads.
When checking accelerator-pump operation, remember there should be no clearance between the actuating-lever screw and the diaphragm lever at idle. When adjusted properly, the diaphragm lever should be able to move enough beyond WOT to accommodate a 0.015-0.020-inch feeler gauge as shown in the photo.
All gasket surfaces should be cleaned carefully with a wire brush to remove old material.
Use a wide-blade screwdriver or a jet-removal tool when replacing a jet. The wrong-sized screwdriver could damage the jet's orifice and affect the flow.
Work in a clean environment to prevent debris from entering the open carburetor, and remember to blow out all passages with air before reassembly.