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Old 12-15-2007, 05:07 PM
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edelbrock/carter/webber 4bbl carb

ok how do i word this so it doesnt sound stupid... looking into an elderbrock 4 bbl carb the secondary throttle valves have a extra set of valves over top of these what do these do? would it do any harm to have them held open or remove them totaly. holley carbs dont have these. just thought it would give it more air flow. also would it be possible to shave off the choke horn up to the needle valves for more air flow? have to rebuild them anyway

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Old 12-15-2007, 05:24 PM
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The secondary air valves (air velocity valves) control the air speed of the air going into the secondary barrels when you floor the gas petal. This prevents the motor from getting a sudden big gulp of air without any fuel flow. The fuel is heavier than air and resists getting moving (inertia). The air moves easily. the fuel wants to lag. That momentary lag in fuel flow as the secondaries open, is what feels like a bog when you rug it. The velocity valves increase the velocity of the air so to increase the initial pull (pressure differential) on the secondary fuel flow for a smoother transition from closed secondary throttles to open throttles. If you remove the velocity valves, the motor will bog momentarily as you get into the throttle. it may even stall or backfire. When they are open at WOT they are not much of a restriction to airflow. No need to remove them.
The velocity valves are mounted on a shaft with special shaped and offset and weighted counter weights on each end that regulate how the velocity valves react to secondary airflow when the throttles are opened. Modifying the counterweights will change how much,how fast and how soon the valves open.
If you get carried away by lightening the counter weights you will get a throttle bog. If you want to experiment with the secondary air valve counterweights, best to get another one to play with.
Carter used to have different ones for specific OEM applications but I believe the aftermarket Carter and Edelbrock ones are all the same.
Yes you can improve the total carb airflow by removing the choke horn and adding a K&N stub stack (AFB) to the top of the carb. jetting may need be adjusted.
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Old 12-15-2007, 05:33 PM
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phew. ok i guess i wont mess with those valves then. i have a B&M style scoop for the dual setup thanks for the info
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