Vacuum advance

[bcgreen]

I have the 2.7MFI RS engine and I noticed this morning that it was not connected, it either fell off or was intentionally left off. How important is it to be connected?

[E Sully]

Timing is specified at 0' TDC 900 rpm with vacuum line attached. It is a vacuum retard unit, so timing advances 10' when you push on the gas pedal and engine manifold vacuum drops. It helps the engine run cleaner at idle. If it is not connected, you have to take this into account when setting the timing. It is important that max advance is not exceeded.
If the vauum pod is working, you should see the change with a timing light when you connect and disconnect and plug the vacuum line.

[dicklague]

Originally Posted by bcgreen

I have the 2.7MFI RS engine and I noticed this morning that it was not connected, it either fell off or was intentionally left off. How important is it to be connected?

The vacuum advance is for emissions to provide retard at idle and a little cleaner burn. I would leave the advance disconnected if it were my car, and I do have a 1973 2.7 MFI engine so I have been through all of this stuff.

You could set idle to start, but you really want 34 to 35 degrees of advance at 6000 RPM. This is the key target. The mechanical advance on the distributor should should have all this 34-35 in by 3000 RPM.....4000 at most.

You do run it up to 6000 static with the car in neutral.....but it is just a blip. Don't hold it there. I like to use a tach in the form of an automotive multimeter in the rear compartment hooked to the points. A timing light that lets you set the advance dials on the light is handy. Set 35 degrees and blip the throttle to be sure the marks for TDC line up at 6000, and actually get there at 3000-4000.

[E Sully]

This is the centrifugal curve for the Carrera distributor with no vacuum.
dicklague, from the information on this chart full advance is not till about 5,700 rpm. At 3-4,000 advance is only around 26' and still increasing.

[bcgreen]

Originally Posted by dicklague

The vacuum advance is for emissions to provide retard at idle and a little cleaner burn. I would leave the advance disconnected if it were my car, and I do have a 1973 2.7 MFI engine so I have been through all of this stuff.

You could set idle to start, but you really want 34 to 35 degrees of advance at 6000 RPM. This is the key target. The mechanical advance on the distributor should should have all this 34-35 in by 3000 RPM.....4000 at most.

You do run it up to 6000 static with the car in neutral.....but it is just a blip. Don't hold it there. I like to use a tach in the form of an automotive multimeter in the rear compartment hooked to the points. A timing light that lets you set the advance dials on the light is handy. Set 35 degrees and blip the throttle to be sure the marks for TDC line up at 6000, and actually get there at 3000-4000.

Dwell is @ 35 and I am sure timing is not far off. I will have to check it once the wife gets home so she can run it up to 6K. My timing light is not a back dial type, but I don't think it is really necessary since the 38°BTDC notch is easy enough to see. I am guessing since I have never had a back dial timing light, that that type of timing light is good for when you cannot visualize the timing notch or it is none existent.

[bcgreen]

Originally Posted by dicklague

The vacuum advance is for emissions to provide retard at idle and a little cleaner burn. I would leave the advance disconnected if it were my car, and I do have a 1973 2.7 MFI engine so I have been through all of this stuff.

You could set idle to start, but you really want 34 to 35 degrees of advance at 6000 RPM. This is the key target. The mechanical advance on the distributor should should have all this 34-35 in by 3000 RPM.....4000 at most.

You do run it up to 6000 static with the car in neutral.....but it is just a blip. Don't hold it there. I like to use a tach in the form of an automotive multimeter in the rear compartment hooked to the points. A timing light that lets you set the advance dials on the light is handy. Set 35 degrees and blip the throttle to be sure the marks for TDC line up at 6000, and actually get there at 3000-4000.

I can see where the back dial would be handy because you are just blipping the throttle, but in my case, without the back dial, it will have to be held there for a second or two until I read if everything lines up. I am guessing it shouldn't hurt the engine to hold the 6K rpm.