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Old 12-15-2009, 02:21 AM
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No Vacuum at Idle....

Well first off everyone I would like to say thanks to everyone that helped me with my last issue... New one this time... 1984 Dodge 1/2 ton 4x4.... 318 with maybe 8,000 miles on last rebuild. Went to do a little tuning on it today and hooked a vacuum gauge up to vacuum port on the carb and at idle it has 2 to 3 inches.... this engine just has an edelbrock performer cam in it, performer 600 CFM card, 340 heads that are ported and polished, and performer intake. Nothing special. makes great power and alot of torque. Now again at idle there is very low vacuum but just off of idle it jumped up to 15 inches. I connected to the vacuum port on the drivers side of the carb... I was not connected to ported vacuum. And then I connected it directly to manifold vacuum on the #8 intake runner where my power brakes are hooked up and it had about 12-13 inches. I have a feeling that my main circuit is runnin at idle cause the exhaust smells a bit rich but it idles fine for the most part and runs fine. Think maybe my full vacuum port on the carb is plugged? Thats about the only thing I can think of.... Well thanks for you time again.

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Old 12-15-2009, 09:14 AM
Technical Support Barry Grant
 
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Quote:
Originally Posted by hotroddin78
Well first off everyone I would like to say thanks to everyone that helped me with my last issue... New one this time... 1984 Dodge 1/2 ton 4x4.... 318 with maybe 8,000 miles on last rebuild. Went to do a little tuning on it today and hooked a vacuum gauge up to vacuum port on the carb and at idle it has 2 to 3 inches.... this engine just has an edelbrock performer cam in it, performer 600 CFM card, 340 heads that are ported and polished, and performer intake. Nothing special. makes great power and alot of torque. Now again at idle there is very low vacuum but just off of idle it jumped up to 15 inches. I connected to the vacuum port on the drivers side of the carb... I was not connected to ported vacuum. And then I connected it directly to manifold vacuum on the #8 intake runner where my power brakes are hooked up and it had about 12-13 inches. I have a feeling that my main circuit is runnin at idle cause the exhaust smells a bit rich but it idles fine for the most part and runs fine. Think maybe my full vacuum port on the carb is plugged? Thats about the only thing I can think of.... Well thanks for you time again.
Does that carburetor have a ported and constant vacuum source? You may be checking it on the ported vacuum souce which will show little to no vacuum.
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Old 12-15-2009, 02:05 PM
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If you read the post I clearly said I am NOT connected to ported vacuum... I know that ported is above the throttle blades and will not show vacuum till the blades are open. I was connected to constant vacuum. I have never run any truck with the distributor connected to the ported side... I always run them on constant vacuum. And that Is the same line I hooked the gauge up to.
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Old 12-15-2009, 02:11 PM
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Quote:
Originally Posted by hotroddin78
If you read the post I clearly said I am NOT connected to ported vacuum... I know that ported is above the throttle blades and will not show vacuum till the blades are open. I was connected to constant vacuum. I have never run any truck with the distributor connected to the ported side... I always run them on constant vacuum. And that Is the same line I hooked the gauge up to.
Was only trying to help since nobody else had/has responded...not even our product but still trying.....sorry....

Did not catch that early this morning but unless the port is blocked you will have the same vacuum at a constant port that you have in the engine. If the car is too rich that the excess fuel or low timing is causing low vacuum it will be low wherever you check it.
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Old 12-15-2009, 02:20 PM
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I know you were trying to help. I apologize for coming off rude. I do appreciate it. Anyway the thing I don't understand is how it would have nothing at idle but then as soon as I open the throttle it jumps to 15.... I mean that would indicate to me that the port is not plugged but IDK. Its very strange. maybe I should just rebuild the carb and see what happens??? Oh the other thing that leads me to believe its running on the main circuit is that I turned both idle mixture screws ALL the way in and the truck kept running... With the drivers side one all the way in it didn't even miss a beat and with the passenger side one all the way in it kinda slowed it down but not really. think maybe those passages are clogged requireing me too have to use excess throttle for it too idle? hence the crappy vacuum and the rich smell outta the exhaust due to it runnin on the main circuit to stay alive?
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Old 12-15-2009, 02:23 PM
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Quote:
Originally Posted by hotroddin78
I know you were trying to help. I apologize for coming off rude. I do appreciate it. Anyway the thing I don't understand is how it would have nothing at idle but then as soon as I open the throttle it jumps to 15.... I mean that would indicate to me that the port is not plugged but IDK. Its very strange. maybe I should just rebuild the carb and see what happens??? Oh the other thing that leads me to believe its running on the main circuit is that I turned both idle mixture screws ALL the way in and the truck kept running... With the drivers side one all the way in it didn't even miss a beat and with the passenger side one all the way in it kinda slowed it down but not really. think maybe those passages are clogged requireing me too have to use excess throttle for it too idle? hence the crappy vacuum and the rich smell outta the exhaust due to it runnin on the main circuit to stay alive?
It seems strange but when you see the high vacuum numbers in the runner is it also at idle when you dont see any at the carb port?

How much timing does the motor have in it at idle and what rpm is it idling at? How much duration at .050 does the cam have. Are you idling with the front butterlfies open and the rear closed or are they split?
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Old 12-15-2009, 02:27 PM
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Also where exactly is this port located at on the Holley that you are taking the reading from? Metering block? base plate? front ? rear? Our carbs have 2 small ports side by side in the base plate with one ported and the other constant and then a large one in the back but I am showing some of the Holley stuff have up to 4.
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Old 12-15-2009, 02:29 PM
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Its idling around 800 rpms... It was idling when I hooked the gauge up straight to the manifold.... The cam is 270 advertised duration and 204 @ .050. so its very mild. it idles on just the front butterflies open.... the backs won't open till about 1/2-3/4 throttle. This thing is blowin my mind too.
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Old 12-15-2009, 02:30 PM
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Quote:
Originally Posted by hotroddin78
Its idling around 800 rpms... It was idling when I hooked the gauge up straight to the manifold.... The cam is 270 advertised duration and 204 @ .050. so its very mild. it idles on just the front butterflies open.... the backs won't open till about 1/2-3/4 throttle. This thing is blowin my mind too.
How much base timing at idle?
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Old 12-15-2009, 02:31 PM
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Oh its an edelbrock carb... the way it is set up is on the passenger side of the motor looking at it is the ported vac. port, then center is the pcv valve hookup, then drivers side is constant vac. they are all on the front of the carb
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Old 12-15-2009, 02:32 PM
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oh yea sorry.... I believe its around 8 Adv. haven't checked it in a while and was going to yesterday but my timing marks are all dirty and I can't see them..... need to get em cleaned up and try again
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Old 12-15-2009, 02:34 PM
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Quote:
Originally Posted by hotroddin78
oh yea sorry.... I believe its around 8 Adv. haven't checked it in a while and was going to yesterday but my timing marks are all dirty and I can't see them..... need to get em cleaned up and try again
Get them cleaned up and try raising the base timing in the 12-14 at idle and then readjust the mixture screws and see what happens. Also see how much vacuum you have at the pvc port compared to the front port as those readings should be the same if the front port does not have an issue.
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Old 12-15-2009, 02:36 PM
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Also when you are doing the timing marks bring #1 to TDC and verify the marks on the balancer as well.
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Old 12-15-2009, 02:36 PM
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Alright i will get some work done on it and get back to ya... thanks for your help
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