Opps, thats actually a 12v Zener regulating the voltage (voltage input varies between 12.6 and 14.4v)
Using a 4.7v Zener in reverse at D1 seems to give me a nice stable 0.7v at pin1, (this is only the reference voltage so i'd assume that 0.7v is perfectly acceptable.
However i have just made a bit of a breakthrough, i set the Pot so that the LED output was on at idle RPM (only just a few revs less would put the light out), then i applied a small amount of heat to all of the components none made any difference untill i reached capacitor C2, this almost instantly put the LED out, and i found that i could heat and cool C2 to turn the LED on and off.
I'm using small round orange capacitors, are there any less susceptable to heat?
Thanks for the help
Paul