Quadrajet - Chevelle Tech
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post #1 of 28 (permalink) Old Apr 9th, 19, 11:47 AM Thread Starter
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Todd
 
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Quadrajet

I installed a 800 cfm stage 3 from jet quadrajet carburetor on my 454 last year before I put the car away for winter, on 3/4 to full throttle the engine would bog down a little then kick in like a rocket, I was told to adjust the secondary plates, that they may be opening to soon causing quadrabog. The engines runs awesome. I need to adjust Allen head with set screw. Is this the way to get rid of the quadrabogging and will it be eliminated. I can tell that it wants to go
Thanks, Todd
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post #2 of 28 (permalink) Old Apr 9th, 19, 1:26 PM
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Re: Quadrajet

There is no guarantee that "tightening" the secondary air valve will stop the bog. BUUUUUUUUUUUT, this is a very likely cause of your bog. I would recommend tightening the spring tension a little at a time, drive, repeat. If the spring tension on the secondary air valve is too loose, then this is very possibly the cause of the bog.
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post #3 of 28 (permalink) Old Apr 9th, 19, 1:39 PM
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Re: Quadrajet

I'd check into how the mechanical advance is working too, and where it is kicking in.

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post #4 of 28 (permalink) Old Apr 9th, 19, 2:15 PM Thread Starter
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The advance check out good, the engine advances to about 30 degrees when I bring the rpms up, set at about 10 degrees btdc
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post #5 of 28 (permalink) Old Apr 9th, 19, 2:18 PM Thread Starter
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I will adjust set screw more
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post #6 of 28 (permalink) Old Apr 9th, 19, 4:50 PM
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Re: Quadrajet

Hold the tension screw when you unlock the set screw. Or know exactly how many turns it has before it unwinds ! BTDT... when Tom says " a little" , we're talking 1/8-1/4 turn here; its a very subtle setting.
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post #7 of 28 (permalink) Old Apr 9th, 19, 5:43 PM Thread Starter
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Re: Quadrajet

ok, I will give it a try
Thanks
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post #8 of 28 (permalink) Old Apr 9th, 19, 6:21 PM
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Re: Quadrajet

The choke pull-off release time also plays a big part in the opening rate of the secondary air valves (flaps). The ideal release time is between one and two full seconds. Push the plunger in and let go and time it. The are ways to slow it down if too fast. It must not be defective either (must hold vacuum). This and about 3/4 turn of the air valve adjustment screw should yield smooth opening of the secondaries if your jetting is close and ignition timing good.
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post #9 of 28 (permalink) Old Apr 10th, 19, 6:53 AM Thread Starter
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That sounds logical. It's a brand new carburetor, I got it from jegs on line . Jet builds it. It has a ver strong suction at idle, I guess this is normal. I will check into the plunger but not exactly sure how to adjust it.
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post #10 of 28 (permalink) Old Apr 10th, 19, 8:41 AM
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Re: Quadrajet

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The choke pull-off release time also plays a big part in the opening rate of the secondary air valves (flaps). The ideal release time is between one and two full seconds. Push the plunger in and let go and time it. The are ways to slow it down if too fast. It must not be defective either (must hold vacuum). This and about 3/4 turn of the air valve adjustment screw should yield smooth opening of the secondaries if your jetting is close and ignition timing good.

Your experience mirrors mine, although I have had combinations and carburetors that liked a looser secondary valve. 3/4 turn seems to be about right for most.
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post #11 of 28 (permalink) Old Apr 10th, 19, 9:59 AM Thread Starter
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I did turn the set screw a total of 3/4 of a turn took 3 tries so far, it is better. Should I keep turning more, a little at a time?
My neighbors think I'm crazy getting on it to test.
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post #12 of 28 (permalink) Old Apr 10th, 19, 1:24 PM
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Re: Quadrajet

Have you checked the release of the time of the vacuum can?
Did the timing stop advancing at 30? Could used a little more timing unless you're into pinging.

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post #13 of 28 (permalink) Old Apr 10th, 19, 1:44 PM Thread Starter
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Not sure what you mean vacuum can???
Is that on the carb? can advance it more, no pinging
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post #14 of 28 (permalink) Old Apr 10th, 19, 2:55 PM
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Re: Quadrajet

the choke pull off or vacuum break is on the right side of the carb airhorn assy.installed with 2 screws on the airhorn. it has a rod that attaches to a slotted lever on the airvalve shaft. usually vacuum can refers to the vacuum adv on the dist
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post #15 of 28 (permalink) Old Apr 10th, 19, 3:03 PM
von
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Re: Quadrajet

I think he means the choke pull-off release time. The choke pull off is the round pod on the pass side of the carb with a vacuum line attached. The air valve (flaps) tension is set by turning the screw slot in the end of the flaps shaft. That adjusts the spring tension holding the flaps shut. First you loosen the small allen head set screw under it then adjust the spring tension by turning the flap shaft (with a screwdriver) so the flaps are barely held closed by the spring tension. Then turn the shaft clockwise against the spring tension an additional 3/4 turn or so and while holding there with screwdriver, tighten the allen head set screw. To check the choke pull off release time, with engine off push the plunger in all the way that comes out the back of the pull off. Time how long it takes for the plunger to come out all the way on its own.
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