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Hagerty Employee

About time you checked your engine's ignition timing?

Exactly when the spark sparks, lights a fire in the combustion chamber and makes some power and noise is important because these things take time. The timing of exactly when that spark happens is important to how the engine runs, its performance, fuel consumption, and crucially, its well-being.

I got rid of points on most every vehicle I could by putting in the magnetic breaker less set up. Hated having to clean/file/re-gap and replace points all the time, especially if you drove a lot. They would really wear out. I upgraded an old Vega I had like that, before I dropped a 327 under the hood. Still kicking myself for letting that one go. It was a Real Red Light Sleeper.
Pit Crew

Pertronix is an easy to upgrade to electronic ignition and reasonably priced.
New Driver

Nice article. I've put petronix ignition in all of my old cars, eliminating the points. Points generally close up over time due to the heel wearing, which causes the lobe to meet the heel later, retarding timing. All things equal, a closing points gap retards timing, and a wider gap advances timing. Some old Bitish twin bikes make use of that principle, requiring a slight adjustment of one set of points to sync the timing together for each cylinder. Vacuum advance works under light load, high vacuum conditions, and it retards ignition under high load when the intake vacuum drops, avoiding detonation.

Don’t assume you are in time even with an electronic distributor.

Wear on many distributors can get your timing off and it goes not hurt to check it once in a while on higher model cars.

A minor but important correction: A voltmeter or test light across the points WILL show voltage while they are open.
Community Manager

Correct! We have addressed this. 


I still remember running across my first dual point distributor and timing it.
Pit Crew

I gave up on points about 30 years ago. My 68 Shelby KR ate them like candy!
Intermediate Driver

from the article "As the throttle opens and load on the engine increases (it works harder), then pressure in the inlet manifold drops, which in turn advances the ignition timing at the distributor."

Exactly backwards. It is called "vacuum advance" because it advances the timing when the vacuum increases (less throttle), not when the vacuum decreases (more throttle). To prove my point, check the timing at idle (high vacuum). Then disconnect the "vacuum pipe", block it so you wont have a vacuum leak into the engine and check the timing again (low vacuum). The second reading will be less advanced than the first.

Low pressure happens at points of carbureted ported vacuum at all open throttle positions no matter engine speed or load so pressure does not increase at the carb port and vacuum remains at the advance diaphragm. Your right if your pointing out manifold vacuum applied to the advance diaphragm.
Intermediate Driver

Mr. Hanlon, if disconnecting the vacuum advance causes your ignition timing to retard at idle, then your vacuum advance is mistakenly connected to MANIFOLD vacuum.  It should be connected to PORTED vacuum instead.   PORTED vacuum is found on one of the vacuum ports on your carburetor.  It should supply vacuum to the distributor's vacuum advance only when the throttle is open.  The more throttle, the more PORTED vacuum, and the more the ignition timing is advanced.  The only time vacuum should be routed to the distributor at idle is if your car has a ported vacuum switch--a device designed to send MANIFOLD  vacuum to the distributor as the engine is warming up.  When the engine reaches operating temperature, then PORTED vacuum is restored to the distributor's vacuum advance.  This was a commonly used device in the 70's and 80's.

Intermediate Driver

I agree with your PORTED vs. MANIFOLD connection.

However, the article said "The second is a vacuum advance system consisting of a vacuum pipe connecting the distributor to the inlet manifold.", not PORTED vacuum.

In BOTH cases as the vacuum supplied to the distributor increases, the timing advances and as the vacuum supplied to the distributor decreases the timing retards.