1985 suzuki intruder spark problem?

I have a 1985 intruder that is only producing spark when you first hit the starter button. After the starter motor is turning fast there is nothing until you let the button go then it somtimes get one more shot of spark. I have replaced the plugs, plug wires, battery and the coils seem good since it has a good spark jump at the start. Anyone have any ideas?

steve
April 2007