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Rochester B, BC, BV Accelerator Pump

The later Rochester B, BC, BV carburetors used a replaceable cup. In rare cases the carburetor may have a pump with a round stem and a leather cup. These accelerator pumps do not have a replaceable cup and you will need the complete accelerator pump. As shown in the photo, the old pump on the left has a round shaft with a leather cup. Replace the left pump with the accelerator pump on the right . To be 100% sure measure the length of your old pump from the top of the stem to the bottom of the leather cup. That should match the newer replacement pump (2 7/16″)

Accelerator Pump

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.

Rochester B Accelerator Pump
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.


Polish the pump well with 2000 grid or finer sand paper, or polishing cloth. You want the pump to have a smooth glide. Apply a few drops of oil to the cup before installing. That along with the gas will cause the cup to swell up. This will take a few miles of driving. Once the cup is wet don’t let it dry out as that will ruin the pump.

This pump AP120 is included in our carburetor kit, K1144


Rochester Accelerator Pump Illustration
The illustration shows how the accelerator pump assembly is put together. #34 is the return spring, 66-15. #32 is the delayer spring 67-3
#33 is a retainer 90-36 that goes on top of the spring, then the lever #30 85-123 is inserted into the slot at the top of the accelerator pump.

If your carburetor uses a check ball at the bottom of the accelerator pump well, then use the smaller aluminum check ball.

rochester B round shaft pump
The later model Rochester B, 1 barrel used a round shaft type of accelerator pump. In fact two different sized round shaft accelerator pump.


When we refer to the size of this pump we are talking about the overall length. AP327 – 2.851. AP462 – 2.776

Our premium kit K1141 includes the replaceable cup for this type of accelerator pump and the cup works for both round shaft pumps.

This pump uses a return spring 66-15. and a delayer spring 66-44

Rochester B Leather Accelerator Pump

Some of the Rochester B’s with the round shaft had a leather cup. This cup cannot be replaced with the rubber cup. In these rare cases you will need to purchase the complete accelerator pump using one of the part numbers illustrated above.
Do you have a pump that looks like this? If so, then use the K1144 kit plus the 90-36 retainer. These don’t come up very often, but when it does you will know what to do.


Rochester B Pump

Rochester B Pump

Watch a video about how to test the Rochester B accelerator pump:
Rochester B Accelerator Pump
Illustrates the different in return & delayer springs on the 2 types of Rochester B carburetors.


A – Return spring on all Rochester B carburetors. The return spring goes under the accelerator pump. This helps return the accelerator pump to the top position. 66-15
B – Delayer spring on the round accelerator pump stem (late) type of carburetor. The delayer spring goes over the pump stem. A retainer then goes over the stem. 66-44
C – Delayer spring on the flat accelerator pump stem (early) type of carburetor. The delayer spring goes over the pump stem. A retainer then goes over the stem. 67-3

The aluminum ball sits at the bottom of the well, at least in the models that use it. When the pump is pushed down, the pressure of the pump holds the ball down and forces the fuel out the exhaust hole into the main discharge. There cannot be anything holding the ball down, or it wouldn’t allow the fuel to fill when the pump is rising. If the fuel is feeding back into the well, then the check ball isn’t sealing. It should be the aluminum ball. Tap the ball lightly with a brass punch to seat it. If by chance the ball is coming out of the hole completely, then look at the return spring to see if it is keeping the ball from coming out. You may have to spread the bottom of the spring out to fit better.


Some of the B’s have the intake ball on the bottom of the float bowl next to the well. A screen fits over the ball. Again it cannot be held down.
Rochester B Main Discharge
Updated on 11/16/2021

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