My car backfires at 50 mph.
Hi there. There is a timing problem with your engine. Check the vacuum advance to see if its advancing when the engine is at a higher rpm. Also check the spark plugs (https://www.yourmechanic.com/services/spark-plugs-replacement) and wires (https://www.yourmechanic.com/services/ignition-cable-spark-plug-wires-replacement) for if they are...