Holley 847 & 897 Carburetor Technical Support

Watch a video about how to rebuild the Holley 847 carburetor.

Holley 847 Carburetor

The Holley 847 choke plate has a poppet valve. The purpose of this valve is to open on start up so that the air isn't choked completely causing a too much fuel condition. Make sure the poppet valve is not sticking. Remember that only vacuum is used to open this valve.

Just the opposite from above. With the valve missing, there may be too much air entering the carburetor in a cold engine condition thus starving the engine of necessary fuel. If you have a "hard to keep running when cold condition" check out the choke valve and poppet valve. When cold the poppet valve will be closed.

Holley 847 Carburetor Manual: Frequently Asked Questions

Here are some frequently asked questions about the Holley 847 Carburetor, based on the provided manual:

General Information and Design

• What is the Holley Model 847 carburetor? The Holley carburetor Model 847 is a single-barrel downdraft unit designed for Ford six-cylinder passenger car and commercial vehicle engines.

• What are some key features of the Holley 847 carburetor? It incorporates engineering features like a main jet that meters fuel during normal cruising, a fully automatic vacuum piston type power enrichment system for high power, and an accelerating pump with a spring overriding feature for smooth acceleration. It is fully sealed and balanced, with air bleeds and vents open only to filtered air, and the float chamber is vented to the carburetor air inlet for balanced air pressures. Some versions also include passages for balanced vacuum control of spark advance or a vacuum-operated engine speed governor.

• What are the major subassemblies of the Model 847 carburetor? Model 847 carburetors are composed of three major subassemblies: the air horn assembly, the main body assembly, and the throttle body assembly.

Application

• What vehicles use the Holley 847 carburetor? This carburetor model is manufactured in two sizes (847-F and 847-FS series) and is used on all Ford six-cylinder passenger cars from 1941 to 1950 models, and Ford six-cylinder trucks from 1941 to 1950 (except cab over engine trucks). The T-847-HGC series is a larger, governor-equipped version used on 1948 to 1950 six-cylinder Ford buses.

• How can I identify different series of the 847 carburetor? The linkages and levers help identify the carburetor. For example, the 847-F series (1941-1947 'G' series) has a ball and socket connection at the choke and throttle levers and no threaded hole for a distributor vacuum line fitting. The 847-FS series (1947-1950 F-1 through F-6 'H' series trucks) also has ball and socket connections, while the 847-FS series for 1947-1950 'H' series passenger cars has a ball and socket at the throttle lever only. The T-847-HGC series (1948-1950 bus) is easily identifiable by its larger size and the governor housing on the throttle body.

Operation

• How does the float system work? Fuel enters through the fuel inlet needle valve. The float rises and falls with the fuel level, and its lever controls the needle valve, allowing only enough fuel to pass to maintain a specified fuel level in the float chamber.

• How does the main metering system operate? At normal cruising speeds, airflow through the venturi creates a pressure drop. The higher pressure in the float chamber forces metered fuel through the main metering system and out of the main nozzle in the venturi. Air from the high-speed bleed mixes with the fuel to form an emulsion, improving vaporization.

• What is the function of the idle system? At idle and low speeds, when the main metering system isn't effective, the idle system uses high manifold vacuum to provide a pressure difference. Fuel flows through the main jet and idle tube, mixing with air from the idle air bleed, and is discharged from the idle discharge hole below the throttle plate. The idle adjusting needle controls the idle mixture.

• How does the power enrichment system work? The power enrichment system provides added fuel for high power operation. When high power demands reduce manifold vacuum, a spring expands to open the power valve, allowing additional fuel from the float chamber to join the main metering system's fuel flow, enriching the mixture.

• What is the purpose of the accelerating pump system? The accelerating pump system supplies fuel during the brief interval when the throttle is opened suddenly, and before other systems can provide the proper fuel-air mixture. When the throttle closes, fuel enters the pump well. As the throttle opens, the pump rod moves down, compressing a spring that forces fuel through the pump discharge needle valve and out a calibrated restriction into the air stream.

• How does the choke system function? When starting a cold engine, the choke plate closes to confine manifold vacuum within the carburetor, drawing a rich fuel flow from the idle and main metering systems, preventing hard starting or stalling. A spring-loaded poppet valve allows some air to prevent flooding. A fast idle mechanism increases idle RPM during choking. The T-847-HGC series for Ford buses uses a Sisson automatic choke that adjusts based on engine temperature.

Overhaul and Disassembly

• What is involved in overhauling the carburetor? A proper overhaul involves complete disassembly, thorough cleaning of all parts, inspection for wear and damage, replacement of defective parts, and careful rebuilding and adjustment to ensure optimal performance.

• Are special tools required for overhaul? Factory-approved special carburetor tools are strongly recommended to prevent damage, but the carburetor can be overhauled with ordinary tools and reasonable care if special tools are unavailable.

• What are some tips for disassembly? Take plenty of pictures during disassembly to aid reassembly. Use separate containers for parts of the three major subassemblies (air horn, main body, throttle body) to facilitate cleaning, inspection, and reassembly. A cookie sheet with rolled edges can also help keep small parts organized.

• How do you remove the three major subassemblies? First, remove the fast idle rod and pump link. Then, remove the air horn to main body screws and carefully lift off the air horn assembly, being cautious not to catch the float. Discard the air horn to main body gasket. Finally, remove the throttle body to main body screws and separate the main body assembly from the throttle body assembly.

• How is the throttle plate reassembled and adjusted? Scribe a line on the throttle plate during disassembly to align it correctly. Install the throttle plate screws snugly, but don't tighten them fully. Move the throttle lever through its full range of travel; if it moves freely, tighten and stake the screws. If it binds, tap the casting and recheck.

• How is the idle adjusting needle set? Install the idle adjusting needle and spring. Turn the needle in gently with your fingers until it seats, then back it off exactly three-quarters of a turn. Avoid forcing the needle against its seat, as this can groove the tip and prevent correct idle mixture adjustment.

• How is the choke plate reassembled and adjusted? Insert the choke shaft and then slide the choke plate into its slot. The poppet valve spring should face the fuel line connection. Install the choke plate screws snugly but do not tighten. Move the choke shaft lever through its full range of motion; if it moves freely, tighten and stake the screws. If binding occurs, tap the air horn and recheck.