Submitted by Roy Cail.
Question:
My Model A is running a little rough with a lot of backfiring when you step on the accelerator. Can you give me some idea where to start looking?
Ever ask yourself this question? — I have!! Les Andrews provides some tips you may want to consider to eliminate this problem.
Answer:
Back firing is usually caused by the condenser failing, or the points may not have sufficient gap. Make sure they are set at .018 to .020”. Make sure they are not burnt.
Backfiring can be caused by intermittent firing of the ignition system or very lean fuel mixture. If the car has been setting for a while, the carburetor float valve may be sticking. Clean the float valve good and set the float level. Backfiring due to intermittent ignition can be caused by a frayed wire on the bottom side of the distributor plate . . or .. by intermittent connection of the ignition switch.
Potential Solutions:
- Check point setting first.
- Replace condenser next (unless you are using modern points). Make sure the condenser you buy is the right length, some are too short, and that it is good quality.
- Check that the carburetor float valve is operating correctly.
- Sometimes the pop out type ignition switches get intermittent. As a last resort, replace the ignition switch/cable.
- Check the GAV to make sure it is not set too lean