Carb vacuum issues
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Intermediate
Joined: Mar 2014
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Carb vacuum issues
once again I need help, I have a 454 in a 78 vette with a Rochester quadrojet, there are no ports that are ported, I have vacuum on every port all the time , so I am having issues with the vacuum advance with the distributer, do I need to use a vacuum switch in the manifold to achieve vacuum once the car is warmed up , not really sure how it all works, or do I have a bad carb, I bought it rebuilt.
Thanks for the help
Thanks for the help
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
once again I need help, I have a 454 in a 78 vette with a Rochester quadrojet, there are no ports that are ported, I have vacuum on every port all the time , so I am having issues with the vacuum advance with the distributer, do I need to use a vacuum switch in the manifold to achieve vacuum once the car is warmed up , not really sure how it all works, or do I have a bad carb, I bought it rebuilt.
Thanks for the help
Thanks for the help
You have no ports that are ported? Huh? Every nipple that is in the base of the QuadraJet is full manifold vacuum as is the fitting in the top of the #8 intake manifold runner. Connect your vacuum advance to any of them.
Drifting
Joined: Oct 2005
Posts: 1,615
Likes: 150
From: Forth Worth TX
Some quadrajets don't have "ported" vacuum. The "ported" part was taken care of by emission equipment.
My 1970 has the original quadrajet, all of the ports are "manifold" vacuum. The "ported" part was taken care of by the TCS solenoid. Manifold vacuum goes to the TCS solenoid all of the time. The TCS solenoid opens and closes based on temperature, shifter position, etc. In my case the TCS solenoid is actually "porting" the vacuum.
Back to your engine, you don't need or really want "ported" vacuum. Assuming that you timed the vehicle correctly, run a vacuum line straight from the carb to the distributor. Adjust your idle screw to achieve whatever idle you desire and you're done.
When you properly time a vehicle with the vacuum disconnected from the distributor and get everything working correctly, you will then re-connect the vacuum to the distributor. Once you do this the vehicles idle will increase a few hundred rpm's. You will then need to re-adjust the idle screw to lower the idle speed back down to where you want it.
How to time a vehicle, http://www.corvette-restoration.com/...ine_Timing.pdf
My 1970 has the original quadrajet, all of the ports are "manifold" vacuum. The "ported" part was taken care of by the TCS solenoid. Manifold vacuum goes to the TCS solenoid all of the time. The TCS solenoid opens and closes based on temperature, shifter position, etc. In my case the TCS solenoid is actually "porting" the vacuum.
Back to your engine, you don't need or really want "ported" vacuum. Assuming that you timed the vehicle correctly, run a vacuum line straight from the carb to the distributor. Adjust your idle screw to achieve whatever idle you desire and you're done.
When you properly time a vehicle with the vacuum disconnected from the distributor and get everything working correctly, you will then re-connect the vacuum to the distributor. Once you do this the vehicles idle will increase a few hundred rpm's. You will then need to re-adjust the idle screw to lower the idle speed back down to where you want it.
How to time a vehicle, http://www.corvette-restoration.com/...ine_Timing.pdf
Last edited by Revi; Aug 18, 2015 at 02:55 PM.
Melting Slicks
Joined: Apr 2007
Posts: 3,189
Likes: 111
From: Tolland CT
Some quadrajets don't have "ported" vacuum. The "ported" part was taken care of by emission equipment.
My 1970 has the original quadrajet, all of the ports are "manifold" vacuum. The "ported" part was taken care of by the TCS solenoid. Manifold vacuum goes to the TCS solenoid all of the time. The TCS solenoid opens and closes based on temperature, shifter position, etc. In my case the TCS solenoid is actually "porting" the vacuum.
Back to your engine, you don't need or really want "ported" vacuum. Assuming that you timed the vehicle correctly, run a vacuum line straight from the carb to the distributor. Adjust your idle screw to achieve whatever idle you desire and you're done.
When you properly time a vehicle with the vacuum disconnected from the distributor and get everything working correctly, you will then re-connect the vacuum to the distributor. Once you do this the vehicles idle will increase a few hundred rpm's. You will then need to re-adjust the idle screw to lower the idle speed back down to where you want it.
How to time a vehicle, http://www.corvette-restoration.com/...ine_Timing.pdf
My 1970 has the original quadrajet, all of the ports are "manifold" vacuum. The "ported" part was taken care of by the TCS solenoid. Manifold vacuum goes to the TCS solenoid all of the time. The TCS solenoid opens and closes based on temperature, shifter position, etc. In my case the TCS solenoid is actually "porting" the vacuum.
Back to your engine, you don't need or really want "ported" vacuum. Assuming that you timed the vehicle correctly, run a vacuum line straight from the carb to the distributor. Adjust your idle screw to achieve whatever idle you desire and you're done.
When you properly time a vehicle with the vacuum disconnected from the distributor and get everything working correctly, you will then re-connect the vacuum to the distributor. Once you do this the vehicles idle will increase a few hundred rpm's. You will then need to re-adjust the idle screw to lower the idle speed back down to where you want it.
How to time a vehicle, http://www.corvette-restoration.com/...ine_Timing.pdf
The "ported" vacuum was put in place to address emissions, retard ignition when at idle, runs hotter.
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Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa