While driving on a tour one day, your Model A produces a loud backfire and soon after, your normally smooth running engine starts acting up. After checking “things” out, you’re still not sure what the problem could be. Someone says, “Could it be the condenser?” Usually the reply is “How can one tell?” The course of action usually is to remove the condenser from the very hot engine compartment and just try to replace it with another one while not getting burned. Or, if your distributor has modern points with the condenser located inside the distributor body, the only way to change it is to replace the whole distributor. Not a simple job on a hot engine while on the side of the road.
A simpler way of checking if it’s a bad condenser is to remove the distributor cap, body and rotor. Make sure the points are closed. Turn the ignition switch on and place the high tension wire (from center of coil) about one-half inch from any convenient ground on the engine. Push points open with a screwdriver then close. The spark should jump the gap with a sharp crack and a straight line. The spark should have a blue tinge.
If the condenser is bad, the spark will still jump the gap, but will be thin and stringy and white in color. Whenever in doubt, throw the condenser away, especially if it is a new reproduction condenser. These cannot always be depended upon. If you happen to have used condensers and want to have their condition checked, maybe your local TV or radio store will still have the necessary equipment to check them for you.
Why not try this while your Model “A” is running great. Then you will be able to reference what a good condenser’s spark should look like.
HOW TO CHECK A BAD CONDENSER