Question about final timing

[bonnietiler750]

The car does run now many thanks to all for your help in this, I have not completed final timing though, do I complete this with the Vacuum advance connected or disconnected?

[sujitroy]

If a non -Federal US car, you can keep it connected.
Sujit

[Goldstar]

UK car - disconnected. Rev the car with the light on to check you get more advance which will tell you your dissy is functioning as advertised.

[sujitroy]

If a non -Federal US car, you can keep it connected.
Sujit

I got it wrong then

[trunt]

I got it wrong then

I think the federal with retard is done connected as it’s at idle that the retard is actually active. advance cars are done disconnected, but a federal with retard deleted would also be done disconnected.

Terry

[mallardstag]

When disconnected block off the vacuum port to the carb for smooth running whilst setting the timing.

[Goldstar]

When disconnected block off the vacuum port to the carb for smooth running whilst setting the timing.

Interesting. Never done that and never had any problems. What’s the theory behind it?

[mallardstag]

Interesting. Never done that and never had any problems. What’s the theory behind it?

My assumption was that with the vacuum advance disconnected to the now open vacuum pipe will then draw excess air into the system upsetting the mixture.

[Lingen]

An open vacuum pipe would make the fuel mixture leaner, but as has been said, there is no point in removing the pipe as there is no vacuum in it when the engine is ticking over.
Mike.

[mallardstag]

An open vacuum pipe would make the fuel mixture leaner, but as has been said, there is no point in removing the pipe as there is no vacuum in it when the engine is ticking over.
Mike.

Thank you for the that. I assumed that some vacuum is required to get the mixture into the cylinder (even at idle). Is it that it's too small at idle to make any difference? Just trying to understand this.

[Wheelz]

Thank you for the that. I assumed that some vacuum is required to get the mixture into the cylinder (even at idle). Is it that it's too small at idle to make any difference? Just trying to understand this.

The vacuum supply for the distributor is 'ported' and so it's not quite the same as the vacuum in the inlet manifold. The position of the throttle determines how much vacuum is applied to the distributor, which is zero with throttle closed, and this increases to full manifold vacuum as the throttle valve opens.

Vacuum in the inlet manifold varies depending on engine speed and throttle position. For example at WOT (wide open throttle) the vacuum is minimal, but at high revs, with throttle closed (overrun), is maximum.

[mallardstag]

The vacuum supply for the distributor is 'ported' and so it's not quite the same as the vacuum in the inlet manifold. The position of the throttle determines how much vacuum is applied to the distributor, which is zero with throttle closed, and this increases to full manifold vacuum as the throttle valve opens.

Vacuum in the inlet manifold varies depending on engine speed and throttle position. For example at WOT (wide open throttle) the vacuum is minimal, but at high revs, with throttle closed (overrun), is maximum.

That makes sense, thank you, nice to learn something new.

P.S. bonnietiler750 apologies for hijacking your thread.

[trunt]

Even so, the butterfly is never truly closed, so it’s usually considered best practice to remove and block the port..

[stag8manod]

I run 4 barrel Eidelbrock with a vacuum gauge fitted. At idle it pulls 22 inches and ai full throttle it's 0 or heading into positive pressure.
Cheers Ian A

[mallardstag]

I run 4 barrel Eidelbrock with a vacuum gauge fitted. At idle it pulls 22 inches and ai full throttle it's 0 or heading into positive pressure.
Cheers Ian A

Is that at the distributor advance port which is what I was referring to?