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Discussion Starter #1 (Edited)
I am a novice, shade tree mechanic and I seem to know enough to get myself in trouble.
I had been using a 735 cfm Holley and recently put on a Edelbrock carb and I had same problem with Holley.
I have a 327 that the idle speed picks up for no apparent reason. After idling perfectly, I jazz the engine and the engine speed is slow to come down and it doesn't. I back off the idle adjustment and then it comes down and the engine dies. It seems link the vacuum advance isn't working correctly. I disconnect the vacuum line and the idle goes down, I reconnect the vacuum and it goes back up.
 

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do you have the line for vacuum adv. connected to a full or ported supply.Ported is 0 vacuum until the throttle blades are moved, and thats where you need to be connected..on holley its upper passenger side of carb....try posting questions in specific generation, C2 or C3 ,I assume, since you have a 327 ..you ll get more responses. Welcome to SV
 

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Discussion Starter #3
do you have the line for vacuum adv. connected to a full or ported supply.Ported is 0 vacuum until the throttle blades are moved, and thats where you need to be connected..on holley its upper passenger side of carb....try posting questions in specific generation, C2 or C3 ,I assume, since you have a 327 ..you ll get more responses. Welcome to SV
The carburetor on now is a new Edelbrock 1411, 750 cfm. From what I can tell there are two vacuum ports on the carb. One is for
timed vacuum=vac. adv. for emissions controlled engines and the other is for distributors vac. adv. port for non=emissions controlled engines. Mine def. does not have emissions items on it.

Thanks so far. I will take all the hints I can get.
 

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you want the ported not the emissions. if you have a vac gauge, check each.. should be 0 at idle, and increase with part throttle..I think thats your problem. its on full vac. and as you slow idle down, the vac falls ,lessening adv and engine dies..and when you speed engine up, vac increases ,adv increases and engine idle increases.....how big is your cam?
 

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Discussion Starter #5
thanks for the reply. Yes, I have the vaccum to the correct side. I don't have a vacuum gauge. A friend is bringing one up this weekend. I am going to check the springs, etc. in the distributor to see if one is broken and if the arms are moving freely. It is the original distributor my have updated it to electronics and MSD box for good spark.:cheers:
 

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weak cent. adv. springs could cause the same effect, by allowing adv at idle... you won t be sorry if you upgrade ignition to MSD box.. good luck..
 

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Ported vacuum which is what you want for the dist Vac adv. is obtained from a vacuum port located above the throttle blades, whereas manifold vac on the carb is located on the base plate of the carb. Like Fish says also a vac gauge will confirm this. As a side note have you considered an intake manifold leak? :catfight:
 

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Discussion Starter #8
1) fishslayer - I forgot to answer about the cam ? earlier. The cam @50 intake is 240 and exhaust is 246 with lobe separation of 110.

I checked the distr. springs and arms and didn't appear to be any problem. No drag on the arms while sliding. I plan on Sat. checking the vacuum and putting a T in the line for the gauge while it is running to see what is happening then.

2) hot rod - I have considered the manifold leak, I plan this weekend to spray some carb cleaner around the manifold to see what happens. Thanks for your help in brainstorming my problem.
 

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thats a healthy cam, with not a lot of idle vacuum..if you are using full vac instead of ported, that will certainly cause what you describe.. also, when you had the cap off, did you make sure the vac adv moves?
 

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Discussion Starter #10
Got the engine to idle. No vacuum leaks. Looks like timing is 10 degrees. Took car out for a test drive and seems like no power. Step on the gas and engine noses over, has a tendency to back fire. Turned around, went back home and shut the garage door.

Any thoughts? :z1-2:
 

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when a engine backfires, it could have several causes...check your cap and rotor first for damage, and that the advance mechanism is working..any chance you have a plug wire burnt or two wires crossed on the wrong plugs? If not, I would do a compression check on all cylinders..you could have a burnt or bent intake valve, or a worn exhaust cam lobe . If you get a low compression reading on one cylinder, pull the valve cover and verify the rockers for that cylinder are moving in proportion to the other cylinders on that side.
 

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Discussion Starter #12
I still need to check the cap and rotor. I put them on not to long ago, but you know how that goes. Wiring looks fine and can't see any burned wires. Could start the car up in the dark and see if there is any cross firing happening. I do need to do the compression check again and possibly a leak down for a bent valve, etc. I hadn't thought about checking the normal lift of the rockers. I am going to check the plugs for fouling carbon. I have wondered about the possiblity of the worn cam lobe. The engine/cam doesn't have many miles, but that doesn't necessarily mean that the cam lobe is worn.

I'll keep checking, thanks again for your thoughts. I initially needed to get the car idling correct and go from there.
 

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Sometimes a worn cam lobe can give you a popping noise thru the carb. Do you hear that? But I am not sure which lobe (intake or exhaust) will make the popping noise (thru the carb) when worn. I think it's specific only to exhaust.

Have you considered the accelerator pump (carb), if it's bad or misadjusted, it will give you a flat spot during accel and will backfire thru carb. Could be you have multiple problems here. But check it out and let us know. Good Luck!!!
 
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