Eric:

If I understand you correctly, you're using too few cells, too low of a voltage for your ignition battery.
I think you said that you're using four cell nicads, ie 4.8 volts?

On my 26CC Evolution, minimum voltage is 6 volts, whereupon the electronic ignition shuts off the motor.
That's to make it safe for using a 2S Lipo for your ignition battery.

I think you want a seven cell NiCd/NiMh or a 2S Lipo for your ignition battery?