The car battery has to put enough energy into the coil for a powerful spark. In the higher rpm range the time to do this is very short, so all conditions have to be perfect for good performance. Make sure you are using the right coil for your engine, see: "What kind of coil do you recommend?" Resistance somewhere in the primary circuit can cause a lot of ignition problems as well, think about the following: - Coil and ignition wiring: Use good connectors and cables of good quality - Ignition key: Make sure the dashboard ignition key is in good condition ( test to power the ignition/coil direct from the battery ) - Ground connection of the distributor: Make sure the distributor makes a good electrical connection with the engine.