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Old 08-31-2008, 05:09 PM
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Holley 4150 question

On the vaccuum secondaries on a holley 670cfm 4150 I have read you can make a 1 minute performance change by switching the spring in the vaccuum canister for the secondaries. Included with my carb was the 2 springs, one painted black on the top and the other painted yellow. Which spring would I put in for an increase in performance ie. which spring would I use to allow the secondaries to open sooner?? I know that one of the springs is intended for better mileage and the other for better performance. Please help if you know anything about this matter.


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Old 08-31-2008, 05:39 PM
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The weaker/lighter spring is for performance. Opens secondaries sooner. Stronger spring delays opening.
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Old 08-31-2008, 05:40 PM
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You select the correct spring by how it runs. If it opens too soon it will have a bog, so you play with the different springs until you get it right.
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Old 09-01-2008, 02:19 AM
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I'd get the spring kit..contains about 6 different springs (all color coded ). Two yellow (or white..Dam CRS).. springs..(one short..one long ) are the lightest and open soonest.
You may need other than the two (and the original spring) you have with the Quick Change kit...for best results.
Spring kit is IIRC $10-$15

You can only test UNDER LOAD. Winging the throttle in nuetral will not/ or should not open the secondaries..
Here is a link to Holley Carb Tuning Manual

As DV said..it's a trial an error method..but because of the quick change kit..and Spring Kit..very easy.
Also..to see if the secondaries are actually opening..put a paper clip on the secondary actuator rod near the top...mark it's placement..if it moves on the rod..the secondaries are opening.

Changing the spring does require you to go out and use the throttle hard.. to test..

So..not a bad job...

Last edited by Docc; 09-01-2008 at 02:24 AM.
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Old 09-01-2008, 06:38 AM
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thatll be a 4160 not a 4150 carb
4160=vacum secondaries
4150= non vacum secondaries
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Old 09-01-2008, 07:43 AM
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Common for the Holley. You know, like the DP VAC SEC 4150 on the 396 Cobra Jet Hemi in the Colony Park Wagon.
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Old 09-30-2008, 03:42 PM
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You have to remember though, you are not supposed to be able to "feel" the secondaries kick in . In your kit it will tell you that the lighter springs(silver & yellow)are for manual trans equipped or lighter vehicles (GVW below like 3000#), and the heavier spring (black) is for heavier vehicles. The lighter ones improve performance and the heavier one improves mileage, but you have to remember how I started this post, you are NOT supposed to be able to feel the secondaries kick in just a smooth increase in power.
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