Here is a mystery. The car is an early 71 that is essentially stock, but I run a header and a Mallory dual point mechanical-only distributor. It starts great every morning and runs well for about ½ hour. Then I get a stalling effect. It is as if one turns the key off and then quickly back on. It happens once or twice at first but then gets more frequent as I go along. I had this problem before and replaced the positive and negative connectors at the coil and it went away. Now it is persistent. By the way, it only affects the engine – voltage does not drop, the lights do not dim, etc. when it occurs. Any help is greatly appreciated.