Previous Toc Next



shaft) provides for a minimum accelerating fuel discharge for warmer climatic conditions.

medium discharge for normal driving and climatic conditions,

c. The No. 2 hole (center) provides a

d. The No. 3 hole provides a maximum discharge for colder weather.


Carburetor service should be performed only with the use of proper equipment. Approved equipment includes fuel level and float setting gages, together with other special carburetor tools. In addition, approved specification sheets must be utilized. Refer to the current Holley Carburetor Catalog Sheet for the carburetor being overhauled to find the proper engine and carburetor specifications.


Road check the vehicle, if possible, before making any adjustments on the carburetor to improve performance. Dragging brakes, poor wheel alignment, low tire pressure, and other causes of undue friction tend to retard engine performance. Evidence of leakage, dents, or clogging in the exhaust system can cause trouble. Check the color of the exhaust for indications of an over-rich mixture, for 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.


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


The fuel system should also be inspected. Examine all fuel lines for clogging, collasped sections, and other damage. Make a manual check of fuel line connections for looseness or leakage. Check the fuel tank vent for possible obstructions. 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 there is one.   Using a vacuum gage, check the fuel pump for air leaks. Connect the gage to the line leading to the pump. A vacuum reading less than 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 fuelpump pressure causes enginetoflood resulting in poor fuel economy. Low pump pressure is associated with a lean mixture and poor performance.


Make a preliminary inspection of the carburetor after first removing the air cleaner. Check the position of the choke plates with the engine running. Throttle the engine down to idle, then completely close both idle adjusting needles. If the engine continues to run for even a short interval after this is done, it usually indicates one or two faults. The tips or seats of the idle adjusting needles maybe damaged, or idle speed set too high, or else there are deposits of carbon in the throttle bores near the throttle plates.

To continue with the carburetor inspection, stop the engine and check the tightness of the carburetor to manifold, and manifold to engine conditions. Inspect all carburetor connections and linkages. Examine the accelerating pump by rapidly opening the throttle and observing the pump discharge nozzles. Each pump discharge nozzle should emit a fine, solid stream of fuel simutaneously with the opening of the throttle.


Check governor housing for leaks, such as holes in castings, loose cover screws and loose fittings. If necessary, remove governor cover and check condition of diaphragm.   A check of the governor and control can be performed by disconnecting governor to control line. With the engine rpm at 2000, place finger on governor inlet hole, if engine governs down, the trouble is in the control valve, and not in the governor.

If by now the trouble has not been located, remove the carburetor from the engine and dis-


Previous Toc Next