Distributor / Vacuum Advance Help

[NJBronk]

Waiting on my carb rebuild kit I’ve been taking a closer look under the hood.

I noticed for the first time that the vacuum advance tube is disconnected. It looks like it should run to the (ported?) vacuum nipple on the carb that is currently capped? I remember reading here that it should be manifold vacuum (otherwise there is no vacuum at idle)? Is this the correct port? Maybe it is manifold vacuum? It’s a Holley 4 barrel. FYI, the advance does move when I suck on the tube.

I believe I set initial timing with the vacuum advance disconnected, right?

There is another vacuum tree with dodgy plugs at the back of the intake. That’s probably a question for another thread…, but I’m guessing PCV system isn’t hooked up?

Back to the distributor…. I believe I have a duraspark II ignition? It’s a 1974. The rotor looks a bit worn. I’m definitely doing plugs and wires, thinking I should at least do a new cap and rotor, but want to make sure I get the right parts. What should I look for? I remember reading that 75-76 had a different cap and rotor? Want to make sure I don’t get the wrong one.

Is there anything else I should proactively replace? Any reason I should replace the whole distributor while I’m at it? They don’t seem crazy expensive, but newer parts sometimes aren’t as good as original.

Thanks!

 

[DirtDonk]

You do have a Duraspark, but it’s been converted to the later model with the blue grommet module. Not a bad thing, but perhaps not done well either.
You can see at least one wire that was not reconnected.

Your distributor is the 75 and later wide version. A 74, or at least most of them would have come with the first generation standard cap and rotor.
You have the more desirable set up.

Yes, you should tune with the vacuum advance disconnected. Even if using ported.
And in most cases, if you are using a direct to carburetor connection, it works better on ported vacuum.
There are very good arguments to using full manifold vacuum, but our rigs often run better connected the other way.
And it is correct, at idle there should be no vacuum on a ported fitting.

That rear vacuum tree center port should be for a brake booster. If present.
Your PCV valve should be plumbed to a common plenum area under the carburetor.

 

[NJBronk]

You do have a Duraspark, but it’s been converted to the later model with the blue grommet module. Not a bad thing, but perhaps not done well either.
You can see at least one wire that was not reconnected.

Your distributor is the 75 and later wide version. A 74, or at least most of them would have come with the first generation standard cap and rotor.
You have the more desirable set up.

Yes, you should tune with the vacuum advance disconnected. Even if using ported.
And in most cases, if you are using a direct to carburetor connection, it works better on ported vacuum.
There are very good arguments to using full manifold vacuum, but our rigs often run better connected the other way.
And it is correct, at idle there should be no vacuum on a ported fitting.

That rear vacuum tree center port should be for a brake booster. If present.
Your PCV valve should be plumbed to a common plenum area under the carburetor.

Thanks!

So what could that unconnected wire be for? The truck ran fine until my carb started flooding…

So I’ll get a cap and rotor from a 75-77.

 

[B RON CO]

Hi, look up a duraspark wiring diagram. The white wire is from the ignition switch, but may not be needed.
You have an aftermarket replacement module from Wells. They were pretty good.
The wide cap and rotor is better, and was made standard on the later cars. The wide design lessens the chance of spark scatter under the distributor cap.
I feel most cars run better using the ported vacuum, the way Ford designed it.
Good luck

 

[billh1289]

I found the attached useful when I was chasing gremlins…