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Carburetors Carb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.

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Old 08-07-2006, 05:39 PM   #1
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Secondaries Not Opening (Carb experts help!!!)

Alright, the other day my dad and I went under the hood to see if we could figure out why my choke light is staying on, and after a little while we noticed the when we reved the engine, the secondaries were not opening. I thought that maybe the car just needed to be warmed up for a while. So we reved the hell out of it, all the way to 7k plus (It was him, not me. I was a bit shaken after hearing my LG4 go to 7k!), and still nothing, even after just letting it idle for 5 minutes or so. To say the least I am semi-lost when it comes to carbs. Why would the secondaries not be opening? I have the stock cc q-jet, nothing special here. There is vacuum going to the controller for the secondaries, maybe the controller's bad? I have no idea.
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Old 08-07-2006, 05:43 PM   #2
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Car: 1984 Z28 Hardtop / 1988 IROC T-top
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The secondary air valve won't open with no load.

If your choke light is staying on all the time, check your alternator.
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Old 08-07-2006, 05:55 PM   #3
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i had a lg4 and the little plastic cam was missingfrom between the metering rods that opened up the secondarys
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Old 08-07-2006, 06:00 PM   #4
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Car: 1984 Z28 Hardtop / 1988 IROC T-top
Engine: 383 Carb / 305 TPI
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Axle/Gears: 3.54 Dana 44 / 3.08 10 bolt

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That plastic cam doesn't open the secondaries, it raises the secondary metering rods when the secondaries are open.
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Old 08-08-2006, 01:09 PM   #5
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Agreed, the secondary air valve doors on top of the secondary bores will never open when free-revving in neutral.

However, there is a way that a choke problem can prevent secondary opening. Almost all QJets (and definitely all computer controlled ones) have a little secondary lockout arm that will prevent the secondary THROTTLE BLADES from opening unless the choke is FULLY open. GM's cheesy way of keeping you from beating on a cold motor. However, if the choke isn't opening fully (let's say the choke element is bad or disconnected or the supply of voltage to it is compromised in some way) it's entirely possible radiant engine heat alone will NOT get the choke hot enough to open fully. And as I said before, if it's not open fully the secondary lockout arm won't allow the secondaries to open. And you get this "secondaries not opening" problem.

Please note this secondary lockout applies to the THROTTLE BLADES on the secondary side, not the air valve doors at the top of the carb. As was pointed out by others the air doors at the the top WILL NOT OPEN just free-revving in neutral- even if the throttle plates below them do!

However, if you find what I wrote is, in fact, your problem and you fix it the difference in WOT performance will be immediate and dramatic- you can clearly tell the difference in performance between no secondary opening and correct secondary opening.
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Old 08-08-2006, 01:09 PM
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