Rochester B, BC, and BV accelerator pump circuit technical information, rebuilding help, and parts guide.
Extra fuel for smooth, quick acceleration is supplied by a double spring pump plunger. Rapid opening of the throttle valve, as in the case where accelerating from low speed, causes an immediate increase in air velocity in the carburetor venturi. Since fuel is heavier than air, it requires a short period of time to "catch up" with the air flow. To avoid a leanness during this momentary lag, the accelerator pump furnishes a quantity of liquid fuel sprayed intot he air stream to mix with the incoming air and maintain the proper air/fuel mixture.
The pump is operated by the combined action of two springs which are calibrated to move the plunger in such a manner that a sustained charge of fuel is delivered for smooth acceleration. The pump is attached by linkage to the throttle lever. When the throttle valve is closed, the pump plunger moves upward in its cylinder allowing fuel to flow through a slot in the side of the pump well into the pump well, through the vapor check ball passage, bypassing the plunger head, and on into the bottom of the pump well. The pump discharge ball is seated at this time to prevent fuel and air from draining into the pump well from the pump discharge passage.
When the pump plunger is moved downward for acceleration, the force of the stroke seats the vapor check ball int he pump plunger head to prevent fuel flow back into the float bowl. Downward motion of the pump plunger forces fuel up through the discharge passage and lifts the pump discharge check ball from its seat and then passes on through the pump jets into the venturi area where it strikes the side of the boost venturi atomizing the fuel with the air and is delivered to the engine.
| YEARS | 1950-1951 | 1952-1962 | 1957-UP | 1963-1968 |
|---|---|---|---|---|
| TYPE OF PUMP | Slotted stem, flat shaft, leather | Slotted stem, flat shaft, leather | Round stem, rubber cup, 2 3/4” | Round stem, rubber cup 2 13/16” |
| FLOAT BOWL SCREW | 10-32 | 12-28 | 12-28 | 12-28 |
The Rochester 1 barrel carburetor used 2 styles of accelerator pumps through the years. One has a flat shaft and the other has a round shaft.
The flat shaft is easy. The same accelerator pump fits all of the early 1 barrel carburetors. Cars to 1956. Trucks to 1962. These were originally a leather cup type (which is ethanol ready) and the current accelerator pumps of this type are still made with leather cups. The leather cup is not replaceable nor is it interchangable with a rubber cup.
This is the round shaft type of Rochester B accelerator pump assembly. The return spring **66-15** goes in the well 1st. The delayer spring **67-3** goes over the shaft. The bracket is next, then a retainer clip, which can be a simple C clip. holds it together.
NOTE: this leather pump and will need to be replaced with a complete pump. You won't find this in many of the 1 barrels, but it does comes along once in a while. Kits only include a rubber replacement cup which will not work on this pump.
To replace the pump measure the overall length and compare with our 2 different pumps.
Our rebuild kit that cover round shaft accelerator pumps include a replacement rubber cup, garter spring, and application tool.
