Holley Accelerator Pump - Team Camaro Tech
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post #1 of 5 (permalink) Old Jul 16th, 00, 04:45 PM Thread Starter
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Chris
 
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Where can I adjust the accelerator pump on my 850 double pumper. I get a little bog off the line when I'm cruising stop light to stop light. Complete Novice when it comes to playing around with carburetors.

Thanks.
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post #2 of 5 (permalink) Old Jul 16th, 00, 06:26 PM
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David Pozzi
 
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Make shure your distributor has a good advance curve first.
Then check float levels and idle mixture.

Then the base setting for the accelerator pump is to open the throttle all the way and check for .020" added movement of the accelerator pump lever against the screw with the spring on it. You don't want the lever to bottom out before the throttle is all the way open. If it bottoms out, it will start compressing the spring. If you have any clearance between spring and lever when at idle, the accelerator pump will not begin to squirt fuel soon enough.
Adjust the screw if it's off.

In tuning it you can change two things:
volume and duration.
If you increase the squirter nozzle size giving more fuel sooner, the pump will reach the end of it's stroke sooner.
So you need to determine exactly when you are having the problem.
If it bogs right off idle, go bigger on the squirter size.
If it goes a while and then bogs, it may actually need a smaller jet to increase the duration.
There are different plastic cams too but I have not fooled with them.

I really need to emphasize that you need the ignition and basic carb adjustments sorted out first, with good plugs, wires, etc.
Then you can start tinkering with the accelerator pump system.
Also make shure the engine and carb are up to temp before tuning it. I've seen Holley carbs need a re adjustment to mixture screws after driving the car about 10 miles. The manifold and carb heats up and the fuel vaporizes more easily and the carb runs a little richer than first was adjusted at home.
David

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post #3 of 5 (permalink) Old Jul 17th, 00, 11:24 AM
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Gene
 
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I am currently reading the "SA" (publisher) book on super-tuning Holley carbs. The author states that the squirter generally does not need to be changed, and to try out different color cams before going to a different squirter. Of course, this assumes that the correct carb was selected for the engine in the first place!
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post #4 of 5 (permalink) Old Jul 17th, 00, 03:32 PM
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David Pozzi
 
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gheatly,
thanks for the tip.
I haven't had to fool with tuning accelerator pumps. It's usually something else out of adjustment.
I'd also check for proper delivery of the fuel through the squirters. and go over the linkage setup. There is a second hole for the pump cam but I can't recall what it's effect is.

Holley carbs are also prone to fine dirt plugging the idle circuts which can cause low speed problems.
Frequently all you need to do is spray the passages out with carb cleaner and blow a little air and carb cleaner through the idle screw holes. And it's good as new.
David

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post #5 of 5 (permalink) Old Jul 18th, 00, 05:49 AM
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Gene
 
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david,

You were right about the ignition though. In the chapter on carb modifications, the author states that one of the first things you should do before tuning or modifying the carb is to make sure the ignition is in proper working order.

The SA Designs book has been very helpful and I would recommend it to anyone that wants to learn more about Holley carbs.

With respect to the pump cams, the different cams are shaped to change the timing and size of the pump shot. High performance engines typically need more of the shot up front and less on the back end. This is because high performance cars are usually built to allow the engine to rev quickly (low weight, rear gear selection, etc). Because engine RPM can increase quickly, the main metering circuits begin flowing fuel faster.

The squirter is used to change the duration of the shot. They do not change the size of the shot and, if chosen improperly, can affect the timing of the shot. Longer duration pump shots are required in heavy vehicles that accelerate slowly. Because the engine RPM increases more slowly, it takes longer for the main metering circuits to kick in. Therefore, the "hole" in the fuel curve that the accelerator pump must cover is longer in duration.
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