Reply To: RD-17 bottom plug fouling – no high speed power

[frankr]

You gotta stop and consider how the magneto works. Here is the simple, non-engineering-degree version. For the time being, forget about the vacuum switch. As the flywheel magnets pass by the coil laminations, electricity is generated in the coil’s primary winding. That electricity flows from one end of the coil to the other end. Called a “circuit”. Electricity leaves one end of the coil, goes to the points, and they being closed, the electricity goes to ground. Then it flows through ground to the ground lead on the other end of the coil (remember—a “circuit”). At a certain time, the points open, and that breaks the circuit, setting off a chain of events that results in spark voltage sent to the spark plugs.

Now, suppose that coil lead going to the points was shorted to ground. The points could open and close all day and not break the circuit to ground–thus no spark. That is exactly what the vacuum switch does. In event of high manifold vacuum, the vacuum switch closes, which shorts the points lead to ground, and the cylinder stops getting spark.

That’s about as simple as I can say it. Next, you get the written test.