Secondaries Not Opening - Team Camaro Tech
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post #1 of 6 (permalink) Old Jul 13th, 06, 05:47 PM Thread Starter
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Secondaries Not Opening

The engine is a stock 350 in my son's Chevelle-nothing special.The carb is a Holley 1850-2 600 cfm vacuum secondary.The secondaries will not open under any circumstances.The carb has been rebuilt and works fine other than this problem.The engine pulls 18in vacuum at idle.
He's getting fed up and impatient,talking about a swap to quadrajet.I'd like to help him get the Holley working before he goes to all the trouble of changing intake and carb.Any ideas?

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post #2 of 6 (permalink) Old Jul 13th, 06, 11:30 PM
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Re: Secondaries Not Opening

What make u say the secondaries will not open?
A quick blip no load will not open them..
If on the highway and u feel them open, then that means they are set wrong
What is happening in this case is its leaning out, power drops off then sec open, and away.
A well setup holly has a smooth transition.

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post #3 of 6 (permalink) Old Jul 14th, 06, 03:41 AM
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Re: Secondaries Not Opening

In addition to Steptoe's suggestion, place small tyrap onto the secondary diaphram shaft directly underneath the housing touching the housing.

Go for a road trip. Lift hood and check position of tyrap on shaft. If it has moved, secondaries have opened.

Another cause for not opening is the secondary plates may be stuck closed in the bore. If this is the case, you may have to remove the carb from the manifold and screw up the setscrew on the passenger side of the throttle base plate on the secondary side. Open it just enough to keep the secondaries from sticking close. You will have to reset the curb idle lower because you've opened the throttle. The sec's don't need much, maybe a 1/4-1/2 turn of the screw will prevent the sec's from sticking.

There is also a secondary spring kit and you can install a weaker spring to pull in the secondaries.

Holley secondaries only open when the demand from the engine is needed. A heavy car with a low numerical rear gear is a prime example. If WOT is given, then the secondaries will open sooner on a full size car than on a smaller compact car. Engine rpm has alot to do with secondary opening. Anything below 5K rpm, they usually don't open up in a light car.

An old racer's trick is to put a screw and nut into the driver's side linkage and use the mechanical linkage to pull open the secondaries. You will see a linkage rod going from the primary to secondary slot. As you open the primaries to full throttle, the rod slides in the secondary slot. Add the screw & nut before the rod so the rod bumps against the screw and pulls the secodaries open. Be prepared for a bog at low rpm.

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post #4 of 6 (permalink) Old Jul 15th, 06, 10:42 PM
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Re: Secondaries Not Opening

Peter, you can rev the engine while looking at the carburetor with the car sitting still and will NEVER see the secondaries on an 1850 or a 3310 open! They come open on engine demand (i.e. low vacuum and load pulls them open). You'll never feel them open while accelerating either, unless there's a problem. They were designed that way and they work beautifully. I suspect they're working just fine unless something is blocking the vacuum port on the carburetor body or there is a hole in the diaphragm. Get a Holley Trick Kit and tune the carburetor; the purple secondary diaphragm spring usually works the best, the no-paint spring will probably cause a bog at low speed. The idea is to use the spring with the least tension that doesn't cause a low-speed bog in high gear. And whatever you do, DON'T PUT A SCREW in the secondary linkage--it's there to make sure the secondary butterflies close fully and nothing else. That's why double-pumpers have a secondary pump--to make the transition from lean to full flow when the secondaries open mechanically. If yer desperate enough to put a Quadrajunk on it, geez.............chuckle Good luck!
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post #5 of 6 (permalink) Old Jul 30th, 06, 05:28 AM
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Re: Secondaries Not Opening

I agree with most said here. I've used all these carbs over the years. I've had terrific luck with Quadrajets, but they need to be set up properly.

I've also used the "screw in the linkage trick" on Holleys with vacuum secondaries, but, as stated, this will cause a bog as you are forcing the secondaries to open with no extra fuel enrichment.

I like Everett's suggestion the best, about checking that the secondaries are not sticking shut. There is a small set screw which will help prevent them sticking. Adjust that as Everett says.....................


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post #6 of 6 (permalink) Old Jul 30th, 06, 06:52 PM
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Re: Secondaries Not Opening

Another common cause is the tiny circular cork gasket missing between the secondary diaphragm housing and the carb main body; that seals the venturi vacuum passage from the primary venturi to the secondary diaphragm. If it's missing, the secondaries will NEVER open.

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