When an engine is under a heavy load, a richer air/fuel ratio is needed to produce maximum power, so most carburetors have some sort of enrichment system. some carburetors use a power valve, which is basically an extra jet that opens to supply more fuel when necessary, or tapered metering rods that fit into the jets and can vary the size of the orifice(s) as necessary. Enrichment systems may be mechanically or vacuum controlled.
If you've ever looked down a carburetor as the throttle was opened (hopefully when the engine wasn't running), you probably saw a squirt of fuel being discharged into the venturi. When the throttle is suddenly opened, the air accelerates and in effect leaves the fuel behind for an instant. As a result, the engine goes lean and stumbles. The accelerator pump's squirt prevents that from happening.
Long Live The Holley 94
Often mistaken for strombergs, Holley 94s were used by Ford from 1938-57, which means there were a bunch of them made, and many of them are on classic Ford pickups. The lineage of these carburetors is somewhat convoluted. Henry Ford was looking for a more efficient carburetor than the strombergs his company had used since 1934, so the Chandler-groves Company was enlisted to develop an entirely new carburetor. once it was finished, they were given a one-year contract to supply all the carburetors for Ford's '38 production run. In exchange for that agreement, Ford was given the patent rights on the new design, and when the year was up Henry took the blueprints and went looking for a better price on carburetors. With some minor changes to the design, Holley cut the price by 10 cents apiece and became the sole supplier of 94s until production came to a halt in 1957. While the '38 carburetors are labeled Chandler-groves, Holley made many with the Ford script on the float bowl. some later-model carburetors have a 94 cast into the bowl; they are usually Holley model r-713s or 2100s sold by Holley as replacement carburetors.
Although the 94s and 97s share the same three-bolt mounting pattern and look similar, there are a number of significant differences between the two designs. on the 94s, the fuel inlet is in the top of the float bowl rather than the side of the bowl as on 97s; 94s use a centerhung float compared to the side-hung 97; 94s use spray bars to discharge fuel in the main system; 97s use emulsion tubes. All Holley 94s aren't created equal, either- the original 94 had 0.94-inch venturii, and later y-block versions had 1.0 and 1.062 venturi with a 1 or 1 1/16 cast in the side; cfm ratings range from 155 for the smallest versions to 185 for the largest. After tallying all the variations, when production ended there were at least 17 versions of the 94.
Replacements for worn throttle...
Replacements for worn throttle shafts are available. As the carburetors we were dealing with were in excellent condition, we installed new standard-size extended shafts from speedway.
When replacing the shafts,...
When replacing the shafts, make sure the throttle valves are centered before tightening the screws.once the valves are properly positioned and the screws are tightened, stake them so they can't come loose.
While late-style Holley power...
While late-style Holley power valves (center) will fit a 94, they don't seal properly. on the left is the correct style. often confused with a power valve is a spark control valve that goes on the outside of some carburetors used with load-o-Matic distributors (right).