I have a 63 with Petronix and Edelbrock. Yesterday I adjusted timing according to service manual (disconnected and plugged the vacuum line from the distributor and adjusted to 5 degrees). Car was idling great but immediately when I re-connected the vacuum hose it started to idled roughly. I measured the advance and it was something like 18 degrees, which I guess is the maximum from the vacuum. Is this normal? I pulled and plugged the vacuum hose and took it for a spin and I didn’t notice any difference in performance. My vacuum hose is connected to the right outlet in Edelbrock, left one is connected to AC, I read somewhere that amount of vacuum is different in these two outlets, so question is can I switch them?


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The vacuum line in question should not have the insert from the smaller hose to the larger one so you are looking for a place the smaller hose should  connect to 

I see you already have a hose to the 20-80% vacuum valve —so not sure —that Anders suggestion is correct

i do not see a place to connect a second vacuum hose to the 20-80% vacuum valve as the vacuum diagram indicates 

The diagram Anders posted should be helpful in finding where your hose in question does belong 

By using the Edelbrock carb you have eliminated the —idle up feature of the stock carb ( a vacuum valve on the old stock carb ) 

Your third picture showing the fire wall with a vacuum line cut and an electrical line coming into the engine bay 

That vacuum line —is for the idle up feature that has been eliminated and should be plugged if not being used now 

All possible air leaks must be eliminated for any vacuum system to work as is intended 

All hoses must be in good condition and sealed at all connections 

All major vacuum lines should have hose clamps including those going to the carb 

All smaller hoses should have there ends clipped and reinstalled ( on these old hoses ) to insure a good seal 


- Left side of anything on a car is the driver side. Right side is the passenger side. There seems to be some confusion in some of the replies. 
- There are a lot of vacuum illustrations and pictures on our Help Page under Vacuum Illustrations. Go toward the end of the album and you will see 63 vacuum lines.Click Here for one such illustration. 
- The ports on the front of the carb are for the vacuum advance... nothing else.
- The port on right passenger side is timed/ported
- The port on the left driver side is full/manifold vacuum. 
- To emulate the original factory carb setup you would pull vacuum off the right ported side. Some people, prefer to pull off the left driver side, especially to get car to properly idle at 5 Degrees Advance per shop manual.  Eldebrock themselves tend to recommend using the full vacuum port on the left.  It is best to use what works best for you. 


Distributor vacuum is now connected to passenger side port and it works fine.

I do now see —the broken outlet on the 20-80% valve and that is where that hose should go 

Anders was very right about his suggestion 

Do plug that line until you can replace the broken valve 

That should enable you to drive the car while sorting out your other issues as you go 


There's slight vacuum from the hose when AC is on otherwise there's no suck or pull. I plugged it and everything is working like should. 

The broken nipple on the 20-80% valve could not be seen in the first set of photos 


The vacuum advance will work in both the left and right vacuum ports on the carb but produces more power on the left side of the carb as it improves the cars timing curve over the stock one for more performance 


For me, the vacuum advancer adjusted all 15 degrees at idle when connected to driver-side port. it made the idle rough and car also vibrated in non-cadillac way.

I will fix the port in 20-80 vacuum valve during winter.

I have not read every post in detail and may have missed something, but when you set car idle you want to factor out all other vacuum on the car. Disconnect the vacuum hose off the back of the intake, and plug it up! If any doubt you can even plug the vacuum fitting off back of carb to rake booster. The bottom line is the engine should be at 5 degrees BTDC with no influence from any vacuum devices or vacuum leaks. Once you set the idle best you can with all vacuum shut off. You can start connecting components starting with the distributor vacuum advance. Drive the car, with back of intake still plugged. Worry about getting the AC vac stuff right after you have engine tuned in. Just one other note. Some like to suggest throwing the advance out to 10 or 15 degrees. I agree a bit of advance may help burn our modern gas a bit better but gradually step it up. Try it at 7 degrees... .how does it run...go back down to 6.. any better? If yes keep it there, if not, go up to 8. Just don't throw it out to 10 degrees advance. That might make things seem to run great on the low rpm end, but you are also altering the advance curve to provide that much more total advance went the centrifugal distributor advances kick in at high rpm ... leading to to bad performance in top end and high rpm situations... such as interstate travel!



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