ported vacuum on quadrajet question - Chevelle Tech
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  #1  
Old Jul 9th, 07, 10:34 AM
ringermt ringermt is offline
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Mike
 
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Default ported vacuum on quadrajet question

I have a 70 SS 402/350, th400, and a quadrajet carb and I cannot locate ported vacuum on the carb.

I recently installed a new distributor and currently have my initial timing at 16 degrees with a total of 36 degrees with the vacuum advance unhooked from the distributor and plugged.

The original distributor was hooked into manifold vacuum on the passenger side of the carb.

If I hook the new (MSD) distributor up to manifold vacuum, my rpms rise to close to 2000 because of the vacuum advance at idle. I thought the vacuum port on the front of the carb on the drivers side was ported vacuum, but I have vacuum at idle there too and my rpms rise when the vacuum advance is hooked up here also.

The only other vacuum port I see is on the firewall side of the carb and I have no vacuum here at all, either at idle or with throttle.

What should I do with my vacuum advance line to my distributor?


Thanks!
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  #2  
Old Jul 9th, 07, 10:42 AM
ss3964spd ss3964spd is offline
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Default Re: ported vacuum on quadrajet question

Mike,

How much vacuum do you have at that drivers side front port? Even the ported vacuum sources will have some vacuum at idle, just not very much.

Dan
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Old Jul 9th, 07, 11:11 AM
ringermt ringermt is offline
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Default Re: ported vacuum on quadrajet question

I have 7-8 inches at idle on both ports. They both increase to 16 inches with throttle.
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Old Jul 9th, 07, 11:17 AM
onovakind67 onovakind67 is offline
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Default Re: ported vacuum on quadrajet question

Do you know why the rpm rises when you add in the vacuum advance? Why not just close the throttle blades to bring the idle back down and take advantage of the increased engine efficiency?
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Old Jul 9th, 07, 12:51 PM
Tom Mobley Tom Mobley is offline
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Default Re: ported vacuum on quadrajet question

what onovakind said. set the timing to 16, set the idle speed as you like it, then hook up the vacuum, slow the idle down to where you want it. you'll have to re-adjust the mix screws.
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Old Jul 9th, 07, 1:25 PM
ringermt ringermt is offline
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Mike
 
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Default Re: ported vacuum on quadrajet question

Thanks, that is what I did. It is running ok now.
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