The Stovebolt Site Forums The Shop Area Engine Shop Ballast resister, do I need one?

The purpose of a ballast resistor is to lower the voltage across the points, extending their life. During startup, the resistor is bypassed, to send more voltage through the coil for easier starting. Once the engine is started, the ballast resistor comes into play.

Some coils come with a builtin resistor.

However, Pertronics devices don't even have points.

You might replace the coil with a higher voltage one for better spark, but sluggish under load sounds like a fuel-air mixture problem or a timing problem, not a spark problem.