1978 Other Dodge Models Will turn over fine, won't start

I've replaced the coil, the ECU, starter relay, I've set the air gap in the distributor, still won't fire at all. It's getting plenty of gas. I removed the coil wire from the distributor and held it close to the block to check for spark, but when my wife turns the key, there is only a small initial spark, and then another single spark when she releases thye ignition. While turning over, there is no spark in between...HELP!!