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Old 05-09-2006, 06:20 AM
72NOVA454
 
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Holley Carb Vacuum Secondary Help

Help

my vacuum secondaries on my Holley 4160 carb won't open. I did that test where you put a paper clip type device on the actuatory arm and then go drive the car at wide open throttle, and then look to see if the paper clip moved, and it didnt. I tested the vacuum actuatory off of the car using a vacuum line @ 5-10 inches vacuum and it moved fine, but on the car at WOT it won't actuate. I blew out the vacuum port from both primary and secondary venturis and they are clean. I put a new washer between the main carb body and the vacuum actuator device to make a good seal and no luck. I have the "silver" plain spring inside the actuator housing.

I've been testing it with "no air cleaner" on. that might be the problem. I will test later today with the air cleaner on and see what happens.

It's a 750 CFM carb sitting atop a 468 Hi-Perf BB chevy with a huge cam, headers, dual-plane intake, ported heads, etc.

Who can provide me with more information on how to diagnose this problem?

thanks.

Lee

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Old 05-09-2006, 06:46 AM
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Forgive but I'm no real carb or engine expert. Offhand I definately wouldn't say your carb is too big....if anything it may be too small. Some basic troubleshooting tips in general or thoughts. Can you test the carb on another engine and see if the secondaries open? Have you hooked a vacuum gauge up to the intake manifold just to see what vacuum you're getting? One last thing, can the secondaries open freely by hand? Not binding or being obstructed by a gasket, manifold,ect.?
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Old 05-09-2006, 08:24 AM
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I like to test for secondary operation with a small piece of paper or napkin. Drop a small piece of paper down in the secondary well, drive it hard, then look if the paper is gone.

I had a similar problem and it was a bad top seal on my vacuum secondary canister on a quick change spring kit. But it doesn't sound like you are using a quick change kit.

Holleys don't make a bunch of noise like a Q-jet. You really can't tell by the sound. If your engine is revving over 4000 rpm with a 454, then I bet the secondary is opening.

You most likely need a weaker spring to feed that 454. Try a yellow spring.
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Old 05-09-2006, 12:37 PM
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Quote:
Originally Posted by Huskinhano
Forgive but I'm no real carb or engine expert. Offhand I definately wouldn't say your carb is too big....if anything it may be too small. Some basic troubleshooting tips in general or thoughts. Can you test the carb on another engine and see if the secondaries open? Have you hooked a vacuum gauge up to the intake manifold just to see what vacuum you're getting? One last thing, can the secondaries open freely by hand? Not binding or being obstructed by a gasket, manifold,ect.?
I have 5-10 inches vacuum at idle. the vacuum actuator opens easily when I take it off the carb and connect direct manifold vacuum to the actuator. the secondaries move easily by hand.
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Old 05-09-2006, 12:48 PM
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Quote:
Originally Posted by 454C10
I like to test for secondary operation with a small piece of paper or napkin. Drop a small piece of paper down in the secondary well, drive it hard, then look if the paper is gone.

I had a similar problem and it was a bad top seal on my vacuum secondary canister on a quick change spring kit. But it doesn't sound like you are using a quick change kit.

Holleys don't make a bunch of noise like a Q-jet. You really can't tell by the sound. If your engine is revving over 4000 rpm with a 454, then I bet the secondary is opening.

You most likely need a weaker spring to feed that 454. Try a yellow spring.
that's not a bad idea, but my idea with the hair pin on the actuator shaft works well, I've done it before on other carbs.

At what vacuum is the secondary actuator supposed to start opening. I'm not talking manifold vacuum, I'm talking main venturi vacuum where it is connected to the vacuum actuator. I've checked books and none of them say what amount of vacuum is required to open the vacuum actuator. I'll try it with the air cleaner on next time I'm out and see if that changes anything. I can throw a different spring on there to but I don't think that's the problem. I check the diaphram seal a few times and it looks good, maybe it has a tiny pinhole leak and wont hold a small vacuum. I guess I should change it and see what happens.
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Old 05-09-2006, 04:10 PM
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mine works with any sring.it just works differently. these sites have tons of info.
http://www.bob2000.com/carb.htm
http://www.holley.com/TechService/Instructions.asp
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Old 05-09-2006, 05:25 PM
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It sounds like the internal passageway is plugged.
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Old 05-09-2006, 08:23 PM
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Quote:
Originally Posted by xntrik
It sounds like the internal passageway is plugged.
not plugged. I blew carb cleaner through the passages and saw it come out in both the primary and secondary venturi's.
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Old 05-10-2006, 09:11 AM
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Quote:
Originally Posted by leejoy
not plugged. I blew carb cleaner through the passages and saw it come out in both the primary and secondary venturi's.
Is it suppose to? Both venturi ?

I am stumped. A "tiny pinhole" shouldn't stop it 100%.

Everything checks out perfect, but it doesn't work...... mmmmmmm.

Borrow a carb ?????
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Old 05-10-2006, 09:12 AM
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Leejoy,

Let's first make sure the secondaries can open. Remove the carburetor off of the engine, and take an air hose with a spray nozzle. Look down the primary passenger side venturi. You'll see a small hole that is coming from the vacuum pod. If you blow air past this hole it will create a low pressure (or vacuum) just like the engine would and the secondary butterflies should open. If they do not you'll want to check the o'rings between the pod and body. If they do you may just need to install a lighter spring in the secondary pod to get them to open.
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Old 05-10-2006, 09:22 AM
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Quote:
Originally Posted by leejoy
that's not a bad idea, but my idea with the hair pin on the actuator shaft works well, I've done it before on other carbs.

At what vacuum is the secondary actuator supposed to start opening. I'm not talking manifold vacuum, I'm talking main venturi vacuum where it is connected to the vacuum actuator. I've checked books and none of them say what amount of vacuum is required to open the vacuum actuator. I'll try it with the air cleaner on next time I'm out and see if that changes anything. I can throw a different spring on there to but I don't think that's the problem. I check the diaphram seal a few times and it looks good, maybe it has a tiny pinhole leak and wont hold a small vacuum. I guess I should change it and see what happens.

I seem to recall reading something someplace, sorry I can't be more specific but I recall a problem similar to yours I think it was something to the fact that the carb was a little too small and was pulling quite a bit of manifold vacuum at WOT due to the restriction of the carb. As a result the carb's secondaries was "seeing" that the motor wasn't under much of a load and keeping the secondaries closed because of a mis match secondary spring. Once again, I'm not sure if I'm recalling it exactly. it just be some food for thought.
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Old 05-10-2006, 09:34 AM
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Quote:
Originally Posted by Huskinhano
I seem to recall reading something someplace, sorry I can't be more specific but I recall a problem similar to yours I think it was something to the fact that the carb was a little too small and was pulling quite a bit of manifold vacuum at WOT due to the restriction of the carb. As a result the carb's secondaries was "seeing" that the motor wasn't under much of a load and keeping the secondaries closed because of a mis match secondary spring. Once again, I'm not sure if I'm recalling it exactly. it just be some food for thought.

Actually a small carburetor "Should" have more air velocity traveling past the primary side of the carburetor causing the secondary butterflies to open sooner.
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Old 05-10-2006, 10:46 AM
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Quote:
Originally Posted by Tech @ BG
Actually a small carburetor "Should" have more air velocity traveling past the primary side of the carburetor causing the secondary butterflies to open sooner.

Your right. Now I recall better what I was refering to. It was someone with a 70 Chevelle with a cowl hood. I don't recall the specifics, I wish I could, but I seem to recall he had an issue with carb sizing being a little too small and somehow this was effecting the cowl diaphram not to work right, as in slow opening. Sorry.
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Old 05-10-2006, 08:40 PM
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Quote:
Originally Posted by Tech @ BG
Leejoy,

Let's first make sure the secondaries can open. Remove the carburetor off of the engine, and take an air hose with a spray nozzle. Look down the primary passenger side venturi. You'll see a small hole that is coming from the vacuum pod. If you blow air past this hole it will create a low pressure (or vacuum) just like the engine would and the secondary butterflies should open. If they do not you'll want to check the o'rings between the pod and body. If they do you may just need to install a lighter spring in the secondary pod to get them to open.
dear tech

why remove the carb for that test? I will do that test with the carb installed and try that first. The o-ring, or in this case "washer" between the carb main body and the vacuum pod thing is new and sealing perfectly. I checked that. First I will road test the car again with the air cleaner on. if that doesnt work I will do your air spray nozzle test as you said. If they do open for that test I will change the spring.

oh by the way I tested another vacuum actuator against the one that is giving me trouble. they both opened at pretty much the same vacuum reading (approximately 2 or 3 inches of vacuum they start opening) you can create 5-10 inches of vacuum simply by "sucking" a tube. I installed a "tee" in the tubing so I can connect a vacuum gauge and watch the gauge move and the vacuum pod simultaneously while I sucked through the tube. like I said the vacuum pod starts moving in at around 2 or 3 inches of vacuum with that silver spring.
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