Electronic ignition with distributor vacuum advance

300jk · Dec 21, 2021

I am currently in a discussion with a friend about the Petronix style ignition when used on a tractor that originally had points and vacuum advance. We have several tractors with this style ignition setup. Friend says tractor even with electronic ignition will not run right without vacuum advance. I disagree. My thoughts are the vacuum advance are for a points system, and not used with the electronic system. Thoughts ?

J Hamilton · Dec 21, 2021

What tractor has vacuum advance?

wore out · Dec 21, 2021

Some Ford's and some Oilallovers, for two examples had vacuum advance. To the O.P., the would be no difference, points or E.I., in the desirability of keeping the vacuum advance. That being said many of the tractors that had it from the factory no longer have vac advance due to the difficulty or impossibility of finding a replacement vacuum ''pod''.

John T · Dec 21, 2021

The only thing an EI does is replace the mechanical contact points with an elec switch. The vacuum advance still rotates the plate to change timing REGARDLESS if an EI or Points are used. If an ignition is designed to use vacuum advance I would still use it even if the switching device were EI or points.

John T

300jk · Dec 21, 2021

Ok I understand what your saying maybe. With a Petronix ignition I dont believe there is any advance like there is with points ignition. I dont see how an electronic ignition has anything to do with spark advance as far as the components in the distributor.

MarkB_MI · Dec 21, 2021

The vacuum advance is there to improve fuel economy under low load. The tractor will run just fine without it. That said, I don't think adding a Pertronix unit to the distributor will disable the vacuum advance. The Pertronix unit just replaces the existing points; I don't think it would affect the movement of the vacuum advance.

504 · Dec 21, 2021

I can't think of one reason why you would want to retard the timing at WOT. Too much timing at low speed can cause detonation,(for those who do not know, it will burn holes in your pistons and eat valves) advanced timing can increase power and fuel economy. As stated, electronic ignition just replaces the points and nothing else, till you change the coil and that still seems a waste of money to me.

ss55 · Dec 21, 2021

On cars you leave the vacuum advance in place when you convert points to Pertronix electronic ignition. You could always check the manufacturer's website for the instructions.

300jk · Dec 21, 2021

John I really value your thoughts. This being said if an electronic device is placed over the main distributor drive, and the pickup part of that ignition is mounted solid what part of that vacuum advance is being used ? As far as I know there is no timing advance in any of the electronic ignitions for normal farm tractors. I could be way wrong on this. I dont even see why it would be necessary after changing over from points. Just asking! Please educate me if Im wrong.

Tramway Guy · Dec 21, 2021

If there IS vacuum advance, it acts on the plate that the points mount on. Since the Pertonix kit mounts to the same plate, the vacuum advance will still work same as with points.

The big advantage to Electronic ignition is that there are no mechanical parts to wear out and no contacts to burn and erode over time. Thus the timing does not drift over time.

KCTractors · Dec 21, 2021

I have a 3 cylinder Ford 2000 with the vacuum advance and the Pertronix Ignition, runs just fine.

Jim.ME · Dec 21, 2021

(quoted from post at 21:47:35 12/21/21) John I really value your thoughts. This being said if an electronic device is placed over the main distributor drive, and the pickup part of that ignition is mounted solid what part of that vacuum advance is being used ? As far as I know there is no timing advance in any of the electronic ignitions for normal farm tractors. I could be way wrong on this. I dont even see why it would be necessary after changing over from points. Just asking! Please educate me if Im wrong.

Many distributors have centrifugal advance. The plate the point, or electronic module, mount in is mechanically advanced by weights below it. As engine speed increases the weights move out and advance the breaker plate. For more detailed info on how the system works search centrifugal (or mechanical) advance distributors.

kencombs · Dec 21, 2021

I'm not sure about that brand but all that I've seen in years past just mounted onto the same plate the points were on. And most distributors move that plate with the vacuum advance. So it should still operate. It is really only useful under low load/high speed (relatively high) conditions. Improves fuel usage.

kencombs · Dec 21, 2021

Adding to prev post> for example I'm converting an old flathead Dodge distributor to electronic using parts from a later slant six unit. The reluctor is mounted on the rotating shaft, The pickup is mounted to the plate I mentioned, advance works just like it did with points.

Bruce(OR) · Dec 21, 2021

You lose.
Time is the factor. Time is a constant. Time cannot be sped up nor slowed down with but with one possible exception if you read the bible.
As for the rest of us, we have to deal with a constant. Advancing timing does not mean speeding up the clock. It means getting the spark to fire before the piston reaches a certain spot in the cylinder.
The faster the engine spins, the sooner you need to spark to occur.
Pistons and gas don't care how spark got fired, it just needs to get fired at the right time so the combustion process is completed inside the cylinder at the right time.
Sorry. You lose.

Jim.ME · Dec 22, 2021

Actually, the mechanical advance of some distributors is accomplished with a two-piece shaft. The top section is piloted on the lower section. The weights and springs turn/advance the top, cam section of the shaft as engine speed increases. Changing springs and weights to modify the advance curve is common in the performance side of things. Have you ever taken hold of a rotor button, turned it 20 (+/-) degrees and see it return to the original position? That is the centrifugal advance springs working. In any case, replacing points with an electronic module doesn't change the advance function.

Jim.ME · Dec 22, 2021

Here is the parts breakdown of a Ford 3000 distributor which has both centrifugal and vacuum advance.

Aaron SEIA · Dec 22, 2021

Doesn't the advance rotate the shaft the rotor is mounted on? I think the plate the points/EI unit mount to is bolted solid in the dist housing.
AaronSEIA

Jim.ME · Dec 22, 2021

(quoted from post at 07:51:24 12/22/21) Doesn't the advance rotate the shaft the rotor is mounted on? I think the plate the points/EI unit mount to is bolted solid in the dist housing.
AaronSEIA

I fumbled on that in my post yesterday, and didn't describe them properly. Centrifugal/mechanical advance moves the shaft. If there is no vacuum advance the breaker plate is generally mounted solid to the distributor body. Vacuum advance moves the plate the points or EI mounts on, there would be another fixed plate or mount below the movable plate, as in the drawing of the Ford distributor I posted.

John T · Dec 22, 2021

Thanks for the kind words... The ones Im familiar with placed a ring over the distributor cam that had 4 or 6 etc magnets that took the place of the high cam lobes opening the points.......Then the pickup coil mounted on the plate which rotated if any advance mechanism activated THEREFORE it worked and advanced same as with points no difference....The vacuum diaphram (if so equipped ???) rotated the plate where the old points ORRRRRRRR the electronic pickup coil is mounted SO THE ADVANCE (if so equipped) STILL WORKS THE SAME

Make sense???????

John T

John T · Dec 22, 2021

Thanks for the kind words... The ones Im familiar with placed a ring over the distributor cam that had 4 or 6 etc magnets that took the place of the high cam lobes opening the points.......Then the pickup coil mounted on the plate which rotated if any advance mechanism activated THEREFORE it worked and advanced same as with points no difference....The vacuum diaphram (if so equipped ???) rotated the plate where the old points ORRRRRRRR the electronic pickup coil is mounted SO THE ADVANCE (if so equipped) STILL WORKS THE SAME
Make sense???????

John T

Papaw8 · Dec 25, 2021

As said by some others vacumn advance is only to improve mileage. It only functions at no or light load. It rotates the breaker plate whether points or electronic in the opposite direction of the distributor rotation. The centrifugal advance rotates the upper portion of the distributor shaft that contains the breaker cam or the reluctor in the same direction as the distributor rotation. Higher engine speed needs timing advanced more than at idle speed. Points or electronic doesn't matter. Also vacumn advance may be on ported or manifold vacumn. Ported will not allow vacumn advance until throttle is opened above idle.

Electronic ignition with distributor vacuum advance

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