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Discussion Starter #21
Since im feeling contrarian lately, I like my ported advance. I have tried to tune for full vacuum a couple time and can't get it to idle below about 900 and my gitty-up is gone. Ported I idle about 5-600 and can induce whiplash.
What am i doing wrong?:grin2:

Is the OP saying he was using ported prior to this? If so and the blades were open the port was open. When your carb is right you shouldn't need any throttle open at all to idle well:)
I didn't have the vacuum advance hooked up at all. I tried ported and settled on full manifold vacuum. This allowed me to turn down the throttle blades and provided a much cleaner burning idle.

^I've had the same experience. I have tried full vacuum in both my 67 C10 and the 65 Mustang and each case I went back to ported for a better idle, running condition.

Full manifold vacuum advances the timing at idle whereas ported should have zero affect on vacuum advance. In my mind it's easier to tune a car with less variables and with zero vacuum advance at idle I can get my car to run better and more consistent?
When setting timing, the vacuum advance should be disconnected and plugged regardless of ported/manifold vacuum.
 

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Discussion Starter #23
Interesting article I was recently digesting on the differences between applying ported- vs. manifold vacuum. Written by a former GM/Chrysler engineer: Ported vs. Manifold Vacuum
Bill, that's actually the article I read that convinced me to stick with manifold vacuum!
 

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Full manifold vacuum improved my idle quality significantly, I actually had to back down on the throttle blades to lower the idle a bit.........".
the reason is very simple. With the dist. connected to full manifold vacuum, the timing at idle is advanced enough to give the burning mixture the TIME needed to completely burn which in turn make more power and increases the rpm. Note: today's fuel formula is much more slowly burning that the gas of the 1960's.

You can, as an experiment, accomplish the same effect by disconnecting the advance and advancing the initial,timing to 15-18 degrees. Which is what I do on distributors that aren't equipped with a vacuum advance.


Interesting article I was recently digesting on the differences between applying ported- vs. manifold vacuum. Written by a former GM/Chrysler engineer: Ported vs. Manifold Vacuum
Completely believable except for the part that GM engineers know how to read and write.

;). ;). ;)

Z
 

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My issue is that I installed a more aggressive cam and have had a tough time getting my idle right.
After fixing a vacuum leak in my brake booster (which had me baffled for months), I still have too much idle transfer slot showing to get the car to idle around 750 rpm. I am going to open the secondary transfer slots a tad and try full manifold vacuum. I can't advance my initial anymore (14d) because that puts my total too high.
 

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Interesting article I was recently digesting on the differences between applying ported- vs. manifold vacuum. Written by a former GM/Chrysler engineer: Ported vs. Manifold Vacuum

John Hinkley is a great guy. I've not met him in person but have communicated with him on at least 3 different forums. Very knowledgeable and has some great stories to tell. Former assembly plant manager and engineer. He worked on, among other things, a lot of the lower volume stuff such as Viper, Prowler, Corvette. It's amazing the details he remembers and can rattle off.
 

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I can't advance my initial anymore (14d) because that puts my total too high.
That is an easy problem to fix. I just welded up the armature inside the distributor to decrease the mechanical advance...allowing me to run more initial but leaving total timing the same. The 13L slot is now basically an 8.5L slot. Making that change decreased my mechanical advance from 26 to 17 degrees.
 

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My issue is that I installed a more aggressive cam and have had a tough time getting my idle right.
After fixing a vacuum leak in my brake booster (which had me baffled for months), I still have too much idle transfer slot showing to get the car to idle around 750 rpm. I am going to open the secondary transfer slots a tad and try full manifold vacuum. I can't advance my initial anymore (14d) because that puts my total too high.
Even with a Ford Autolite distributor you can limit the total timing:

restrict the total advance the distributor is capable of by reversing the weights (if it's a stock Autolite distributor), so the more narrow advance slot is being used. Example: if your distributor is now using the 15L slot, you can reverse the weights and use the 10L slot. Your distributors numbered slots may vary, but one will be less than the other one, and the lessor one is what you want to be using in order to limit overall timing a bit more. This switch to the more narrow slot will let you have more initial advance without yourtotal timing being too excessive

Or you can put a small section of tiny rubber hose (like windshield-washer hose) over the pin that limits the advance. Either of these two methods results in the same general outcome., less total advance.

Z
 

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Oh come on, surely there's SOME way to argue about it. :)
Ok, sure. I can't use mine because I don't have any vacuum advance!

I have a stock Ford DUAL point mechanical advance on my factory 390, running tri-power.
They don't have any ported vacuum.

How's that? lol
 

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Even with a Ford Autolite distributor you can limit the total timing:

restrict the total advance the distributor is capable of by reversing the weights (if it's a stock Autolite distributor), so the more narrow advance slot is being used. Example: if your distributor is now using the 15L slot, you can reverse the weights and use the 10L slot. Your distributors numbered slots may vary, but one will be less than the other one, and the lessor one is what you want to be using in order to limit overall timing a bit more. This switch to the more narrow slot will let you have more initial advance without yourtotal timing being too excessive

Or you can put a small section of tiny rubber hose (like windshield-washer hose) over the pin that limits the advance. Either of these two methods results in the same general outcome., less total advance.

Z
I've got a Petronix ready to run billet distributor. I do have their advance limit "thingies", but I don't trust them. They slip over the advance spring mounts and supposedely limit the travel of the advance mechanism. To me they fit sloppy and when checking with my timing light got some weird results.
 

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Well, I tried it. I moved it from ported over to full vacuum. interesting results, at least to me, admittedly still not understanding it fully. It races and I hear some sputter out of the exhaust while it is on the idle cam. Once it comes off the idle cam it is incredibly smooth and if I closed my eyes I could swear it was a prius running. But once I hit the gas you hear the normal 289 exhaust note. Drove it around for a while and cannot tell in difference in power or sound once off idle. But you stop at a light and I can barely hear it.

When it is idling in the garage I still hear a sputter in the exhaust every 3 or 4 seconds. It may be due to having the initial timing set pretty high? Need to play with it some more, but definitely interesting.
 
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