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Old 09-15-2010, 06:51 AM
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Eric, my skipwhite dizzy vac advance was also limited by the screw because the screw ends up closer to the advance arm inside the canister. Make any sense? I actually cut it open because I wasn't happy with this fact and wanted to see why. So, increasing the hg that my vac advance came in at also affected how much total vac I had. It went from 22' down to 5' advance.

Didn't you do tests on your canister a few months ago? You, or someone, posted results showing how the screw affected how soon advance came in.

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Old 09-15-2010, 07:30 AM
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That was I, the thread is a longer one so you need to read along but it explains what I am talking about on the range vs limit difference towards the end.

Pinging on cruise part throttle acceleration?
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Old 09-15-2010, 07:38 AM
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Originally Posted by TubbedCamaro
Sorry I got a little confused here, thought we were talking stock HEI and didn't realize we were talking about an Accel HEI. Ya depending on how far you turn the screw in the vacuum canister, will determine how much advance you'll get out of it. 7 turns will give you full advance, where 3-4 will give you about 10-12 degrees. This is starting with the adjustment screw turned all the way out counterclockwise and then turning it in clockwise the number of turns stated.

But I don't understand what any of this has to do with you having to much advance at idle. I guess before I opened my big mouth, I should have asked a couple of questions.

One, what do you what the timing to be set at Idle with the vacuum advance connected??

Two, how much advance do you want from your vacuum advance??

Third, have you tried setting the base timing at 16 degrees and taking the car for a drive with the vacuum advance disconnected??

You see the problem is your referencing the vacuum signal from the wrong side of the throttle blades. On the manifold side vacuum is highest when the the throttle blades are closed, but as soon as you crack the throttle the vacuum in the intake manifold drops and so does the amount of advance the vacuum advance is adding. Do instead of advancing your timing as the throttle in opened it actually retards your timing as the throttle is opened. That is why your suppose to hook the vacuum advance to a ported vacuum port on the carb, it is a port that doesn't see vacuum until the throttle is cracked. It is the way a vacuum advance was designed to work.
That was then this is now, emmission control was the reason GM used ported vacuum it was a bummer and it does not apply here on his hot rod.
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Old 09-15-2010, 09:26 AM
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Ported versus manifold is a popular debate.

The stock hei vacuum canister can give over 20 degrees, if there is no limiter plate it can make for an unsteady idle so will work better on the ported position. I prefer to limit the travel and use manifold vacuum.
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Old 09-15-2010, 03:26 PM
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Hello guys thanks for comments but even if I readjust my idle and go to ported vacuum I still have a miss on the stupid engine. Idle is always steady one way or the other there is no difference wise using ported or full manifold idle is the same either way. Also on my paper work that came with my summit hei it said to hook up vacuum advance to ported so go figure but I know that is a hot debate a lot of times.

From my understanding between the two the only difference is at idle and once you take off and the throttle blades are open and while cruising they both work the same.

I have spent countless hours for the last 5 months or more trying to figure out what is causing my miss that is not constant but happens on a regular basis mostly at idle and it makes my idle rough here and there and seems like it will almost want to quit but it has never gotten that bad. Also with the came swap the intake has been resealed again and intake manifold leak has also been ruled out.

I have had two different distributors in this thing along with 4 different sets of spark plugs, three sets of wires, three different control modules, three different cap and coil combos and more ground wire added to rule out grounding issues. I have checked the voltage to the hei and its around 14 volts when running so its fine there. Charging system is all new.

I have had two different edelbrock carburetors and my current holley on this thing and it is still there. Carburetor is ruled out. All vacuum hookups have all been checked and I just recently un hooked my plug wires on top of my distributor and pulled them up one at a time and they are all firing just fine.

I guess I am getting of topic in this post but I really don't know what else to check anymore or what other options I have to check things for that issue. I am pretty sick of my engine and its sad my brothers old stock 305 which has over 175,000 miles on it can idle smooth and not miss and has over 15 year old spark plugs in the thing.

Thanks custom10 for the link will read more about it.

Last edited by eric32; 09-15-2010 at 03:32 PM.
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