mohawk_man_1

So i just bought and installed a Holley 600 CFM vacuum secondary carb (P/N 0-80457s) to my stock manifold using an adapter plate from Summit Racing. The carb runs 100% better than my quadrajet did with only minimal tuning, but the secondaries take forever to open and i get a BIG hesitation before they do. In the installation, tuning and adjustment manual, it says that i now have to go out and buy the spring kit from Holley (P/N 20-13) that includes 7 springs of differnt rates. A friend of mine told me that i should just buy an adjustable cover for the vacuum diaphram that opens the secondaries. Any advice or prices/part numbers for that cover?

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fleetmgr

You can get a replacement diaphragm housing cover that allows for spring changes without having to remove the housing from the main body, but I've never heard of an adjustable cover.

Yes, you need the spring kit. But from your description it sounds like they are opening too soon, rather than too late. That's what would cause the big hesitation you describe. You want Holley p/n 20-59 for the quick change cover, available from Summit, Jegs etc.

mohawk_man_1

i used to be able to apply about 3/4 throttle w/ the quadrajet and at least chirp the tires but now 3/4 throttle has practically no power until the engine gets up to speed then you floor it and it gets power, that's why i thought it was opening late

five7kid

Quick Fuel Technologies adjustable secondary housing, http://www.summitracing.com/parts/QFT-63-1/

Much better than changing springs (if you absolutely insist on using a vacuum secondary carb). It controls the opening of the secondaries the right way, by metering the vacuum signal to the diaphragm (basically controls how quickly the vacuum evacuates the diaphragm - the end vacuum will remain the same). You can use a weak spring, close down the needle valve until bog is eliminated (if you can feel the secondaries opening, they're opening too soon), and the secondaries will still open fully.

When you change the stiffness of the spring, you also change the RPMs required to fully open the secondaries. The chart included with the spring kit illustrates this.

fleetmgr

Now THAT is just too cool. Hadn't seen that little gem before, and I completely agree, it's the right way to do it. Holleys should have been built that way from day one.

fleetmgr

One thing to remember about tire chirp...while you might think it's cool, it's expensive. And the adage about breaking traction always applies, as in if you break traction, you're slowing down.

It says nothing about power, speed or anything else. You can make a lawn engine chirp the tires on your car under the right conditions.