Danny F many thanks for the advice, sketch and simulator screen shot. That looks like just the way I will approach it. Although I will not pull the pic off the board to re-programme it, the plan is to re-condition the square wave by dividing the input by 2/9 and providing the 1 pulse per revolution to the display driver. My original plan was to go the divider routs as per the 74HCT92 decade counter as mentioned by Deephaven and SaabFan, and this may be the way I end up doing it. But I am new to Pics and look forward to developing code to get it to work as desired as a training exercise.
Danny, can I ask what programming software you are using, I like the simulator screen shot and info it it displays.
As far as being anywhere near EMC compatible, the distributor will act like a spark transmitter and AM radio will be lost for at least 30 meters, but then, the sound of a radial engine sounds better so that will make up for it
I really appreciate the help, it's real first class advice. Here are a couple of pictures or the ignition CDI unit. The CDI make is a Rexel, Model A-02 and requires 4.8 - 8.4 VDC. I have two Lipo batteries in series (2C) arrangement at 2000 MAH as the power source (hidden in the black box). The engine was scratch built from bar stock on my lathe and mill and took about a year to produce from plans.
Steve