340 Not firing on all cylinders

Find TDC on #1. Hook up your timing light, back the balancer up to 15* BTDC by rotating the engine. Turn the key to the run position, Turn the distributor until the timing light flashes..... Bam you are at 15* BTDC. Tighten the dizzy just snug so it still moves. Start the car and do your tuning from there.