Jim Smart
January 12, 2010

Ignition systems have one of the toughest jobs under the hood of vintage Mustangs. They handle the very precise job of firing spark plugs in concert with the engine's crank and cam timing events. It's called ignition timing, which can easily be written off as an integral part of engine tuning, a necessary evil, but there's more. Improper ignition timing and spark advance can cost you in terms of lost power, poor fuel mileage, and even engine damage. Too much timing can cause spark knock (also called detonation), which hammers pistons and rings under hard acceleration, breaking ring lands and permanently damaging cylinder walls. When timing is late, fuel economy suffers along with exhaust valves and seats.

The Autolite Loadomatic single-point distributor was a Ford six-cylinder mainstay for many years and was used in the '64 1/2-'65 170/200ci Mustang engines. It doesn't work the same way as a V-8 distributor. With an Autolite V-8 single-point distributor, vacuum and centrifugal advance units work seamlessly together, with the vacuum advance handing off to the centrifugal advance as rpm increases. The Autolite Loadomatic doesn't have a centrifugal advance, but instead uses only a vacuum advance that moves the breaker plate depending upon engine load, throttle position, and manifold vacuum. When the vacuum advance goes to work, it moves the breaker plate counterclockwise to advance the spark. Two retard springs move the breaker plate clockwise to retard the spark. Vacuum advance duration depends on how long manifold vacuum is applied to the diaphragm.

V-8 distributors get their vacuum advance from throttled vacuum. Six-cylinder engines get it from a spark control valve (basically a Holley power valve) screwed into the carburetor. The spark control valve is a calibrated spring/diaphragm arrangement, which is held open by a balance of vacuum and spring pressure. As you accelerate and engine speed catches up, manifold vacuum builds enough to open the spark control valve and send vacuum to the distributor. Once everything gets up to speed, manifold vacuum falls and the spark control valve closes, which retards the spark.

Rebuilding the Autolite Loadomatic is simple, calling for bushing and/or shaft replacement depending upon wear. Aside from shaft and bushing, your Loadomatic will also need a vacuum advance unit, plus points and condenser unless you make the wise switch to a PerTronix Ignitor electronic retrofit.

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