Is your car running rough? Adjusting the choke on the carburetor could fix the proble. Here is a step by step guide that will take you through the adjustment.
The carburetor mixes air and gasoline in the needed proportions for different driving conditions. Starting up on a cold morning may call for a mixture as rich as 7 parts of air for each part of gasoline; cruising at a slow, steady speed may call for a mixture as lean as 18 parts of air for each part of gasoline. To do all of this and still not violate current anti-pollution laws, the carburetor must be an extremely complex piece of equipment in your car. Although it is complex, the carburetor is also very durable. Its parts do not wear out as quickly, or need adjustment as often as those in the ignition system.
When the engine runs poorly or refuses to start, the fault is probably in the ignition system, not in the carburetor. Therefore, you should check the ignition system thoroughly before attempting to make any major adjustments to your carburetor. Specifications for the various carburetor settings are printed on a decal located in the engine compartment of every new car sold since 1970. More detailed specifications and instructions are printed in shop service manuals at car dealers nationwide or found in your local public library. Auto part stores should also have these specifications for your car. Over the years, moving parts on the carburetor become worn, passages become blocked by sediment, the gaskets and diaphragms deteriorate. When these things happen, it must be cleaned and rebuilt, or replaced.
Most of the time, it is just the choke that needs adjustment. Most cars have an automatic choke, which slowly opens as the engine warms up. Tap the accelerator pedal when the engine is cold, the choke should open by just a crack. After 5 minutes of running the engine, the choke should be opened fully.
Remove the air cleaner to observe choke operation. With the engine cold, tap the gas pedal once. The choke plate should close fully. If it does not, spray the choke linkage and shaft with solvent until they can be moved freely.
Loosen the three screws on a carburetor-mounted choke, remove the bimetallic spring housing. If there are carbon deposits inside the housing, replace the cover gasket and check the heat tube for exhaust leaks. Replace a suspect heat tube.
If the arm that the bimetallic spring engages is attached to a vacuum piston, be sure the piston moves freely. If not, remove the arm and piston. Clean the piston and its cylinder thoroughly with solvent. Reinstall arm and piston, recheck for binding.
Clean the bimetallic spring with solvent and reassemble the choke. If there is more than one slot on the control arm, engage the spring in whichever slot will close the choke plate completely when the choke housing is set to the proper index mark.
Rotate the choke housing to the proper index mark. Jiggle the throttle to engage the fast idle arm. Choke plate should close tight. Rotate the housing until the plate closes, then tighten three screws. If the plate will not close, replace spring housing unit.
If there is no obvious choke mounted on the carburetor, wiggle the choke plate to identify its linkage. Follow the long link down to its well on the intake manifold. Open the bolts so that the bimetallic spring can be lifted from its well.
Lift the choke from its well and clean the spring with solvent. Loosen the locknut and turn the post with a screwdriver until the index marks are set to the carmaker's specifications. Tighten locknut and reinstall choke in the well.
If the choke plate does not close tight when the engine is cold, open the well and reset the choke. If you run out of adjustment, try to close the choke by bending the connecting link. If the link then scrapes the well cover, replace the choke unit and the link. Chokes without a piston have one or two vacuum diaphragm. When the engine starts, the diaphragm should open the choke slightly. If it does not, disconnect the hose and check for vacuum. Replace a blocked or leaking hose.
