Vacuum Advance
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From: Kennesaw, Ga
Vacuum Advance
Hey, I have a 1974 F250 with a Manual 390, the previous owner put an edelbrock carb and intake on and i guess forgot to hook up the vacuum advance on the distributer. When I floor it it seems that the secondaries aren't doing anything so i suspect the problem is the distributer. Alright so my question is it has two ports on the distributer, which one should i hook up and should i plug the other one. This morning I put a full manifold vacuum hose on the port facing toward the front ( I plugged the one on the top) and it seemed to have a higher idle but still nothing impressive with the secondaries "open". Any advice would be much appreciated!
-Thanks!
-Thanks!
More Turbo
Joined: Sep 2016
Posts: 559
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From: Australian Outback
Secondaries open through engine vacuum not engine speed. If you are watching them with the engine in neutral and the hood up they won't budge.
No dizzy vacuum will rob you of a small amount of economy. Plug any unused ports and connect your dizzy vacuum outlet (nipple n the round thing attached to dizzy) to the small vacuum fitting on the carb. If there is more than one then pick it and plug the other.
No dizzy vacuum will rob you of a small amount of economy. Plug any unused ports and connect your dizzy vacuum outlet (nipple n the round thing attached to dizzy) to the small vacuum fitting on the carb. If there is more than one then pick it and plug the other.
Lead Driver
Joined: Aug 2003
Posts: 7,592
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From: **** hole San Jose ca.
Edelbrock carbs have two front 1/4" vacuum ports. One is straight manifold vacuum an the other is timed port vacuum for the dizzy.
Edelbrock carbs don't respond like Holley carbs.
Orich
Edelbrock carbs don't respond like Holley carbs.
Orich
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Senior User
Joined: Oct 2016
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From: Kennesaw, Ga
Alright so your saying hook the distributer to the ported vacuum, but which port should I hook it up to the top port or side port on the distributer?
Lead Driver
Joined: Aug 2003
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From: **** hole San Jose ca.
Orich
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Senior User
Joined: Oct 2016
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From: Kennesaw, Ga
Yeah I'm familiar with my carb but where should I hook my vac hoses to on the distributer? There are two nipples, one on the top and one on the side.
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Senior User
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From: Kennesaw, Ga
This is is an older picture but I hooked the distributer to the full manifold vacuum.
How do I hook my distributer up?
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Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
You can hook it up however you want but it will require a little specific tuning or compensation for whatever method you choose. I would suggest connecting to a ported or "timed" source of vacuum for now. There will be no vacuum at factory idle RPM. Anything other than idle, the signal will be the same, or near enough.
Manifold vacuum at idle will allow for lots of advance at idle. This will keep temperatures down, but if you have to pass smog for example, forget it. Probably have to reduce the initial timing on the crank running this way, and consequently the amount of advance internal to the distributor. Aftermarket distributors are a lot more adjustment friendly than standard Motorcraft.
Manifold vacuum at idle will allow for lots of advance at idle. This will keep temperatures down, but if you have to pass smog for example, forget it. Probably have to reduce the initial timing on the crank running this way, and consequently the amount of advance internal to the distributor. Aftermarket distributors are a lot more adjustment friendly than standard Motorcraft.
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Tuned
Joined: Jun 2015
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From: Southern OR
I don't even see a vacuum line from/to the dizzy? maybe I'm blind..
Laughing Gas
Joined: Jun 2016
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From: Des Moines, Washington
I think we are missing the fact that the OP is saying he has a retard/advance setup on his distributor.
If that's true, you'll want to use the port on the carburetor that has little or no vacuum at idle and the port farthest from the distributor body. That should give you correct operationbut I'm not sure you have the correct distributor. My '74 390 has a single port distributor and on other emission controls except a PCV valve.
Michael
If that's true, you'll want to use the port on the carburetor that has little or no vacuum at idle and the port farthest from the distributor body. That should give you correct operationbut I'm not sure you have the correct distributor. My '74 390 has a single port distributor and on other emission controls except a PCV valve.
Michael
Lead Driver
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From: **** hole San Jose ca.
If the vac. advance can has two 1/4" nipples then it can be setup for emission specs.
If one nipples point up to the hood that for full manifold vac. the other that point out to the front of the vehicle is timing vac.= no vacuum at low idle.
All this info is on the Edelbrocks web site per the carb p/n
Orich
If one nipples point up to the hood that for full manifold vac. the other that point out to the front of the vehicle is timing vac.= no vacuum at low idle.
All this info is on the Edelbrocks web site per the carb p/n
Orich
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