The Stovebolt Site Forums The Shop Area Engine Shop Finally getting my 2x1 Rochesters Sorted. Accel Pump question.

Thanks to the help from everyone on here, I'm finally getting my 1955 235" running better. It has a Patricks Mid Cam, Offy 2x1, and Two Rochester B's (2-15/16"). 848 head. So It runs much better accept under light to medium throttle and low RPM. The carbs have 58 Jets and I'm about 1-1/2 turns out on the screw. I noticed after I took the air cleaners off that if i gently give it some throttle I dont get a squirt in either carb, it only squirts under quicker heavier acceleration, which I'm thinking is probably my problem under light accel. Anyway to adjust the pump to squirt under light/slow accell?

Jimmy, my duel W-1s don't squirt much either. The truck moves so quickly now with very little throttle movement, the pumps just don't move enough to push fuel out. I am now learning to drive light footed since it takes less effort to get it moving.

I may look into changing the lever length so it moves the pump rod more with less movement of the throttle shaft. I might also change the foot pedal length so I can push down more, right now I only use about 5 to 7% of total movement. It won't change the pump issue, but it will make driving a little better.

Let us know what you come up with, and glad you are enjoying your hard work.

Joe

Thanks for the info, Joe.

I just find it odd that depending on how fast I press the throttle it either squirts or it doesn't. I wonder if making the pump leather fit tighter in the bore would help?

My understanding is that the squirt if for the sudden opening of the choke and burst of air. A more gradual opening is handled by the main circuit by feeding more fuel.

Dennis

There may be nothing wrong; however a different adjustment may minimize the issue.

First, I posted in a different thread how the initial fuel under acceleration FROM IDLE is supplied by fuel in the transition slot, BEFORE the fuel from the accelerator pump. Changing the idle adjustment might help. Or, it may not.

A couple of possibilities that are causing no squirt under light acceleration:

(1) Many accelerator pumps are designed with a "relief valve" to allow air bubbles caused by percolation in the pump cylinder to escape. With the volatility of modern fuel, it is possible the relief valve is not keeping up with the percolation, and slight movement of the pump opens the relief valve, allowing air in the top of the pump cylinder BELOW THE PUMP to escape.

(2) The accelerator pump circuit has a weighted discharge valve preventing syphoning of the fuel when the circuit is not in operation. Like (1) above, the volatility of modern fuel could cause percolation in the discharge passage which would push some of the fuel in the passage back into the pump cylinder. Thus a slight movement of the accelerator pump would cause only air to be pushed by the discharge valve.

Now, before someone suggests sealing the relief valve, be informed that the pumps with no relief valve can be worse; as the percolation cannot be relieved by the valve, which causes the pressure created to push fuel out past the discharge valve when it shouldn't. This can cause the pump to not work under heavy acceleration either, as the pump cylinder under the pump will be empty of fuel. This is why the relief valves were built into many pumps in the first place.

Jon.