You could be one tooth off when stabbing the dizzy in the motor. The motor would start, but the one tooth will put the timing and the timing marks off a few degrees from where the should be. Try lifting the dizzy up and at the same time rotate the rotor till you feel the teeth come free , then rotate the rotor only, clockwise till the dizzy will drop down to the next tooth of the cam gear. When the piston is at TDC the rotor should be just past the # 1 plug wire post about 4 to 5 % to make up for the advance timing of the motor.