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Carburetor service should be performed only with the proper equipment. This equipment should include fuel level and float setting gauges, and special carburetor tools. In addition, the proper specification sheets must be utilized. Refer to the current Holley Carburetor Catalog sheet for the carburetor being overhauled for the proper engine and carburetor specifications.

normal at the idle indicates an air leak or a faulty fuel pump. A careful check should be made of the fuel pump pressure. Excessive fuel pump pressure may lead to the engine being flooded and will result in poor fuel economy. Low pump pressure leads to alean mixture andpoor performance.




Road check the vehicle, if possible, before making any adjustments on the carburetor to improve performance. Dragging brakes, poor wheel alignment, low tire pressures, and other causes of undue friction should be remedied. Evidences of rust, leakage, dents, or clogging in the exhaust system should be corrected. Check the color of the exhaust for indications of an overrich mixture, or excessive oil consumption and compression loss. A rough running engine coupled with a strong odor of gasoline may result from a flooding carburetor. Improper engine temperatures should be corrected. Many faults may be detected by a visual inspection of the engine in operation. Remedy loose or disconnected wiring, leaking fuel and water connections, possible short circuits, and other faults. A further check can be made of faults, such as a slipping fan belt, by listening to the engine while it is operating in all speed ranges.


After a check has been made of the vehicle, the engine should be examined. Check or set the following in accordance with the manufacturer's specifications: distributor breaker points, spark plug gap, ignition timing, condenser capacity, valve settings, intake manifold for leaks, compression, all gaskets, carburetor body and flange screws, and inlet fuel pressure.


The fuel system should also be inspected. Examine all fuel lines for clogging, collapsed sections, and other damage. Make a manual check of fuel line connections for looseness or leakage. Check the fuel tank vent to insure that it is unobstructed. Even a partially clogged vent may cause the engine to cut out after a few minutes of high-speed operation. Clean the fuel pump sediment chamber and the fuel filter, if one is used. Using a vacuum gauge, check the fuel pump for air leaks. Connect the gauge to the flexible line leading to the pump. A vacuum reading less than


Make a preliminary inspection of the carburetor after the air cleaner has been removed. Check the position of the choke plates with the engine running. The choke plates should be fully open if the engine has reached its normal operating temperature. Throttle the engine down to the idle and completely close both idle adjusting needles. If the engine continues to run for even a short interval after this is done, it may be an indication of two faults. Either the tips of the idle adjusting needles or their seats may be damaged, or there may be carbon deposits in the throttle bores near the throttle plates.

Stop the engine and check the tightness of the carburetor to manifold and manifold to engine connections. Inspect all carburetor connections and linkages. A check can be made of the accelerating pump by observing the pump discharge nozzles and rapidly opening the throttle. Each pump discharge nozzle should emit a fine, solid stream of fuel simultaneously with the opening of the throttle. Examine the accelerating pump link to insure that it is correctly positioned.

If it becomes apparent that the above items are not at fault, the carburetor should be removed from the engine and disassembled. Thoroughly clean and inspect each part, using the procedure laid down in the Service Manual. The accompanying chart lists specific carburetor complaints and discusses the various parts which may be at fault. A rigorous cleaning and inspection, coupled with the replacement of faulty parts and care in reassembly, should prevent recurrence of the complaint.


Many performance complaints attributed to the carburetor may be the result of poor driving habits. It will be impossible to obtain fuel economy if the engine is needlessly raced, the throttle is opened suddenly and harshly, and if the vehicle is kept too long in low and second gear.

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