1975 Distributor Advice - Swap from Vacuum Retard to Vacuum Advance (1 Viewer)

[saltfever]

I have a 75 2F with a vacuum retard distributor and I’m swapping to a vacuum advance distributor (19100-61080). My vacuum retard distributor has two wires (red and black) both going to the coil. One to positive side and the other to the negative side of the coil. I don’t have a model number for the vacuum retard distributor or the coil…can’t read them due to fading. The new vacuum advance distributor has a single wire from the distributor attached to the points and the condenser through the body of the distributor.

Question:
Does the wire from the vacuum distributor attach to the positive side of the coil? Is the distributor then grounded to the engine when installed with the clamp? If this is so should the ground wire be disconnected from the distributor? Is a new coil needed?

 

[B y r o n]

What is your reasoning for making this change? Seems you're going backward since the vacuum retard appears to be pointless and the vacuum advance has points. Why do you feel you need a vacuum advance if the engine was set to run a vacuum retard?

 

[Pighead]

Is that a Pertronix in the vac retard?

 

[saltfever]

What is your reasoning for making this change? Seems you're going backward since the vacuum retard appears to be pointless and the vacuum advance has points. Why do you feel you need a vacuum advance if the engine was set to run a vacuum retard?

The vehicle is desmogged, had a Weber carb when I bought it and didn’t run well. Later found out the intake manifold was cracked When I installed a 78 Aisin carb. It seems to run okay but has some hesitation when acceleratin. The Fj40 mechanic used to repair the manifol, and fix an exhaust leak, said I should install a vacuum advance distributor if I wanted better performance.

 

[saltfever]

Is that a Pertronix in the vac retard?

I have no idea. It was like that when I bought it.

 

[saltfever]

I have no idea. It was like that when I bought it.

It looks like it is.

 

[pjohnson]

You may be able to swap it over to the new distributor. Then use Pertronix instructions for the wiring.

 

[Pighead]

Exactly

 

[Pighead]

Why do you feel you need a vacuum advance if the engine was set to run a vacuum retard?

I thought the F engines were intended to run with a vacuum advance distributor, hence the "E-'69/non US" designation

 

[Pighead]

The Fj40 mechanic used to repair the manifol, and fix an exhaust leak, said I should install a vacuum advance distributor if I wanted better performance.

I agree with your mechanic

 

[B y r o n]

The vehicle is desmogged, had a Weber carb when I bought it and didn’t run well. Later found out the intake manifold was cracked When I installed a 78 Aisin carb. It seems to run okay but has some hesitation when acceleratin. The Fj40 mechanic used to repair the manifol, and fix an exhaust leak, said I should install a vacuum advance distributor if I wanted better performance.

You do realize that switching from vacuum retard to vacuum advance means you have to switch where you pick up your vacuum source. Vacuum retard uses ported vacuum where vacuum advance needs direct vacuum.

 

[Catching Neutral]

I have a 1978Cali spec 40 which came with a vacuum retard distributor. I have since desmogged. I converted the existing distributor to vacuum advance using a vacuum advance canister from @4Cruisers. Used a vacant vacuum port from the carb.

 

[brian]

You do realize that switching from vacuum retard to vacuum advance means you have to switch where you pick up your vacuum source. Vacuum retard uses ported vacuum where vacuum advance needs direct vacuum.

false
ported vac for the vac advance.

 

[B y r o n]

false
ported vac for the vac advance.

This is my source for saying to use direct vacuum, the OP did say he was looking for better performance. Besides better performance the engine should run cooler.

 

[brian]

This is my source for saying to use direct vacuum, the OP did say he was looking for better performance. Besides better performance the engine should run cooler.

pretty sure the OP is NA, and that article is discussing forced induction.

 

[Pighead]

Vacuum retard uses ported vacuum where vacuum advance needs direct vacuum.

I'm pretty sure that the vac advance uses ported vacuum as well. I drove mine around that way for years.
And I'm not going to let a motortrend article sway me over the advice of, (not gonna drop names or initials) everybody else

 

[B y r o n]

pretty sure the OP is NA, and that article is discussing forced induction.

This is naturally aspirated:

"Where should the vacuum canister be routed?

There's been a lot of debate whether or not the vacuum canister should be plugged into a ported or direct vacuum source. Internet forums are rife with opinions on both sides of the argument. However, there is a right and wrong way. And it's not an opinion; it's just a fact.

Plugging your vacuum advance into a direct source will allow it to engage at idle, which is good for a number of reasons. Much like cruise conditions, engines run leaner at idle than they do under load. Again, this means the mixture burns slower and needs an earlier spark to optimize the burn. Ensuring that the mixture has a complete burn before leaving through the exhaust port also helps the engine to run cooler at idle. All carbureted cars were set up with direct vacuum to the distributor before more stringent emissions requirements reared their heads.

Ported vacuum sources are a result of emissions laws and manufacturers doing whatever they could to get big V8 engines to pass smog before the incorporation of the catalytic converter. The idea was that by using little to no spark advance at idle, the exhaust gas would leave the cylinder still-on-fire and help maximize the efficiency of antiquated air injection systems. Engines from this era often ran very, very hot, were prone to warped exhaust valves, cracked cylinder heads and all other manner of issues. Using a ported spark advance will still allow the vacuum advance to do its job at steady cruising, but all of the benefits of idle cooling will be lost.

Here's a quick experiment you can try on your car. Plug the vacuum advance into a ported vacuum source and check the idle rpm. Now, switch the vacuum advance to a direct source of vacuum and again check the idle rpm? We'll bet money the RPM increased. Why? Because the additional ignition timing provided by the vacuum canister and full manifold vacuum source allowed the engine to more effectively burn the air/fuel mixture. It therefore produces more power (even at idle) and rpm rises as a result."

 

[pjohnson]

Interesting article. I don't think I buy it.
When you open the throtle your manifold vacuum drops causing vacuum advance to return to its idle position causing your timing to retard. This will cause hesitation and backfiring.

I pulled that from another car forum post.

 

[saltfever]

Thanks for all the insight. I plan on swapping the pertronix and giving it a shot. I’ll let you know how it runs.

 

[73FJ40]

Thanks for all the insight. I plan on swapping the pertronix and giving it a shot. I’ll let you know how it runs.

You should check with Pertronix to confirm the interchangeability of their module between the two dizzys.

I know Pertronix offers different modules for different FJ40 dizzys.