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Discussion Starter · #1 ·
I have an Edelbrock 1405 600cfm carb with an electric choke on a 70 Chevelle 307 with an Edelbrock Performer intake.

If I wanted to delay the opening of my secondaries, could I simply install a stronger Staging Vacuum Spring? Right now the carb as a 4" or yellow spring. Could I simply install a 7" or pink spring to have the secondaries delayed opening?

Thanks in advance!
Fred
 

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I am new to this Edelbrock carb world anyway I've had nothing but trouble of various sorts. I spoke to the tech rep last week about a bog/flooding type condition from a standstill condition to full acceleration. The car while under cruise power with a trip to full power was nice and smooth. The rep suggested I go to a blue 3" spring but failed to explain its purpose I've since installed it and have just begun to experiment. Does that spring work simalar to the power vavles on a Holley? Sorry for tagging on your letter.
 

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Ok, I'll give this a try:

The seconaries open due to air volocity, meaing that at a certain air flow/throttle position the secondaries open. Greg is right in that the rods stage between "cruise" and "power" modes. The step up rod is this carborator has 2 different size steps. The small diameter part of the rod rests inside of the jet and meters idle fuel and light cruise fuel so long as vacuum is high. When vacuum drops below ~ 8", the spring on the rod pushes the rod up out of the jet and provides more fuel. This makes sense since the motor is getting more air and thus needs more fuel. The point at which the rod moves up is controlled by the spring tension (and vacuum). Edelbrock provides 5 springs: blue-3", yellow-4", orange-5", pink-7" and plain-8". Most of the carbs that Edelbrock sells come from the factory with the orange spring.
If you want to delay the opening of your secondaries, then you must increase your primary jet size of go with a smaller tip rod. This will give you more gas but will make the motor run rich.
As for the delay or bog from idle, the Edelbrock rep was almost right. By switching to a blue spring, you would delay the trasition from cruise to power mode until you vacuum was next to nothing. This indicates that you are to rich on your current calibration. A larger tip rod would help your situation. You can also move the pump arm from the center hole to the top hole and see if this helps (less pump volume). Sorry about being long winded.

Brian
 

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If the edelbrocks are identical to the Carter afb like they supposedly are, its a mechanical secondary carb. Your FOOT controls the secondary butterflies and there is a counterweighted air valve that wont open unless there is a certain air flow. The only way I can think of to delay those is to add more weight to the air valve counterweights.

assuming everything is okay, then the air valve probably SHOULD be opening, but its getting lean.. probably use a stronger power piston spring like they've said...

mike
 

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Discussion Starter · #6 ·
Thanks for all the input, on the phone with my local speed shop and will be talking to Edelbrock in the very near future. And hey, I don't care how many tag on, the more the merrier.
Fred
 
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