Distributor Vacuum Advance Routing
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From: Southern California
Distributor Vacuum Advance Routing
My friend has a 302 that was modified in the past with a Holly 4v carb and intake. Whoever did the modification removed the vacuum lines from the distributor.
She says it gets poor fuel mileage, but otherwise seems to run well. I think that if the vacuum advance was working properly, it would improve the fuel economy and performance.
I saw what I assumed to be vacuum ports that were plugged off on both the primary and the secondary. (I don't know if the secondary is vacuum operated, but can find out).
My question is, where should the vacuum line to the distributor be routed from? I don't recall seeing any vacuum plumbing. There is no vacuum booster for the master cylinder, and no other vacuum operated accessories.
She says it gets poor fuel mileage, but otherwise seems to run well. I think that if the vacuum advance was working properly, it would improve the fuel economy and performance.
I saw what I assumed to be vacuum ports that were plugged off on both the primary and the secondary. (I don't know if the secondary is vacuum operated, but can find out).
My question is, where should the vacuum line to the distributor be routed from? I don't recall seeing any vacuum plumbing. There is no vacuum booster for the master cylinder, and no other vacuum operated accessories.
Elder User
Joined: Jan 2000
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From: Gravel Switch, KY
Distributor Vacuum Advance Routing
This has been a subject of much debate in the past. There are two options, a timed port source, which is above the throttle plates, or a manifold vacuum port, below the throttle plates.
Timed vacuum in conjunction with EGR, AIR and modified distributor advance curves was most widely used after emissions became more stringent. Personally I prefer the manifold vacuum source. This allow the use of more advance at idle and cruise rpms, with the advance backing off as the throttle is opened further and the vacuum drops, thus eliminating pinging. Alot of guys here swear by the timed port approach, and I suppose both work as long as the total package is tuned to work together.
DannyP
89 F-150 4x4 former EFI I-6 now carbed 351W, Edelbrock heads,cam,intake,carb.
MSD 6A, ZF, Sterling 10.25 with 3.55L's.
Timed vacuum in conjunction with EGR, AIR and modified distributor advance curves was most widely used after emissions became more stringent. Personally I prefer the manifold vacuum source. This allow the use of more advance at idle and cruise rpms, with the advance backing off as the throttle is opened further and the vacuum drops, thus eliminating pinging. Alot of guys here swear by the timed port approach, and I suppose both work as long as the total package is tuned to work together.
DannyP
89 F-150 4x4 former EFI I-6 now carbed 351W, Edelbrock heads,cam,intake,carb.
MSD 6A, ZF, Sterling 10.25 with 3.55L's.
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FTE Leadership Emeritus
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From: Southern California
Distributor Vacuum Advance Routing
Thanks for the info Danny.
Sounds like the manifold vacuum port should be the way to go in this case. There is no air pump, and EGR is disconnected. I don't think there is an EGR plate under the Holley.
I'm assuming that the vacuum port at the primary venturi's would be the best source since it's a 4v.
Sounds like the manifold vacuum port should be the way to go in this case. There is no air pump, and EGR is disconnected. I don't think there is an EGR plate under the Holley.
I'm assuming that the vacuum port at the primary venturi's would be the best source since it's a 4v.
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From: Virginia
Distributor Vacuum Advance Routing
The port on the passenger side of the carb, up front on the primary part of the carb, pointing straight out is the ported vacuum source. The manifold vacuum source off the carb should be up front, down low under the front bowel, coming out at an angle (hard to see). You can try the manifold vacuum, but with an automatic trans I have trouble tuning the engine this way. The engine rpms seem to be affected more when the tranny is put into gear. When the ported vacuum is used, the engine doesn't seem to "load down" as much when the trans is put into drive.
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Joined: Nov 2001
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From: USA
Distributor Vacuum Advance Routing
On my engine, there is a hole (with no hose nipple) in the top of the back side of the distributor's vacuum diaphram. Of course, the nipple for vacuum advance comes straight out the front. What I am wondering is, was the hole in the back for vacuum RETARD? I have seen diagrams of running both advance and retard vacuum hoses to respectively just ahead and behind of the throttle plate.
What is the little open hole on my distributor's vac pod for?
What is the little open hole on my distributor's vac pod for?
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Joined: Jan 2001
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From: Virginia
Distributor Vacuum Advance Routing
That little hole is probably where the hose nipple was before it was broke off at some time. It is for retard during high manifold vacuum situations such as idle and deceleration. It supposedly improves emissions with the retard feature, but if it runs alright I wouldn't worry about it.
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From: USA
Distributor Vacuum Advance Routing
The tag on my distributor is D60E 12127 AA 5L25. The 12127 corresponds to the correct basic number series for a distributor, the AA is for part number suffix/design change, and the 5L25 breaks out to November 25, 1975.
However, am I to read the D60E as 1976 Fairlane? I.e., read the '0' as an 'O'? If so, my D8KE carburator is from a '78 Edsel!?!
I guess I don't have the correct model line letter codes for the decade of the '70s.
FWIW, Intake manifold is D5AE-9425-DG and 351W block casting says 8H61 1962.
However, am I to read the D60E as 1976 Fairlane? I.e., read the '0' as an 'O'? If so, my D8KE carburator is from a '78 Edsel!?!
I guess I don't have the correct model line letter codes for the decade of the '70s.
FWIW, Intake manifold is D5AE-9425-DG and 351W block casting says 8H61 1962.
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