Holley accelerator pump cam. How and Why to Adjust a Holley Carburetor Accelerator Pump

How and Why to Adjust a Holley Carburetor Accelerator Pump

holley accelerator pump cam

Only do this repair if it's necessary. Please be aware that this is a community forum. An important point should be kept in mind when tuning a double pumper: The secondary accelerator pump must supply fuel for a sufficient time so that the secondary main nozzles can begin to flow fuel to the engine after the secondary throttles are opened. Some are only for use with a 50cc pump. If I open the throttle quickly, I get a lean spot, and my meter reads 16:1 Is this lean spot at a steady throttle hold, and the lean spot is only momentary? The cam basically just revolves around the shaft, the adjustment holes let you fine tune the curve of the cam for your needs. The less opening I have initially when cruising, the more I can reproduce the lean spot. Totally different cams, heads, everything, except the intake and exhaust,and obviously, i don't have a carb.

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Holley Accelerator Pump Cams 20

holley accelerator pump cam

The two types of check valves found under the diaphragm: Ball and bail on left, umbrella on right, from bob2000. Repositioning the cam in this way makes allowance for the extra throttle rotation required to maintain the relatively higher idle setting. Also, if there is a vacuum advance being used and it is hooked to manifold vacuum, the engine can have a slight to a major hesitation if the engine is overly dependent on the increased timing from the vacuum advance. While this is a common modification on automatic-transmission equipped cars, the 50cc is also sometimes a necessity with 2 X 4 tunnel ram applications as well. Pump shooters or nozzles are available from sizes 25 through to 52. It's an acceleration issue when I cruise, and quickly open the throttle a bit. And where would Position 3 of the pink cam go? By the way, you should also be aware of the check valve needle that is underneath each shooter.

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Holley Accelerator Pump Cams 20

holley accelerator pump cam

If a shooter has been drilled out, the number on it obviously will no longer apply. Hope this helps: Pos 1 on cam should be aligned and screwed into carb hole 1. When I have the throttle just cracked, so that it appears that I'm right in the transition slot somewhere, then I get that lean spot when I quickly open the throttle. Holley accelerator pump nozzles are all stamped with a number that coincides with the diameter of the hole size. It would be nice to know all the particulars, as in, what series carb do you have. I don't think there is any sure fire formula on what cam to use. I will assume nobody has made the mistake of blocking the power valves.

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Holley accelerator pump

holley accelerator pump cam

Conversely, a gently sloping ramp will spread the pump action over a longer period of time. First off, your dyno tuner don't know squat. This will remove any raised edges or whatnot that may be causing the check to not seat tightly. In order to get a stock or mildly modified engine to accelerate smoothly, when you push down on the accelerator pedal, you typically need both an advance in ignition timing and an increase in fuel delivery. Conversely, if off-idle acceleration does not feel crisp or clean, then the pump nozzle size may already be too large.

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Confusion in Tuning the Holley Accelerator Pump Cam

holley accelerator pump cam

I did some testing and measurement on a 650 dp and found that if carb hole 2 and cam hole 3 provide 2. I don't know if they were meant to be that way, but it does work if your look for that right profile. Think of it more as a fuel curve. The smaller diameter nozzles lengthen the pump shot duration and are used with heavier vehicles or with vehicles equipped with lower numerical rear axle ratios. In this case a smaller size is required. If there is too much clearance or conversely, not enough clearance , hold the screw at the bottom and adjust the nut at the top of the spring. Now, it seems that I dump too much fuel too soon, I just don't know if I need a pump cam change, squirter change or both.

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Holley Accelerator Pump Cams 20

holley accelerator pump cam

Remember if you change you pump cam to readjust your accel pump linkage, you don't want to over extend it. By my rough estimates, I took them down to about 1. I can reproduce that every time with throttle bursts. I had a stumble with the red cam. Hydro carbons are drastically reduced. For example, this shows the volume in ccs for 10 strokes with a 50cc pump, rather than the stock 30cc pump that I use.

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Accelerator Pump Parts

holley accelerator pump cam

Then I asked about his timing i thought is was suspect too slow. In operation, the accelerator pump is connected by a linkage to the throttle butterfly shaft. Doug Yes I have headers and an H-pipe. In this case, the larger pump capacity will help during the transition. While the dip may be due to the pipes, the only place to address it is at the carb. If your car is experiencing a stumble, begin by first checking the clearance between the pump operating lever beneath the screw and spring and the pump diaphragm arm.

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Accelerator Pump Parts

holley accelerator pump cam

So, if the pink cam has the greatest volume other than the brown , it should also have the largest lift. The squirter size affects the time that it takes for that fuel to be delivered by controlling the actual flow into the venturi. The 50cc pump also uses a larger pump cam -- either brown conventional carburetors , or a yellow color regularly used on 4500-series carburetors. Sometimes, there are two or three numbered holes in each pump cam. The cam profile affects the actual movement of the accelerator-pump lever and consequently, the amount of fuel available at the pump nozzle.

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