I have never run 0 before, I went by the factory sticker under the bonnet, valve clearances have been done, running 98 supposedly but now it is like I am running ethanol blended fuel (91) I am changing fuel stations when this tank is out and following your advice, even the mechanic said his book showes 5 deg + - 2, no I was not blocking off the vacuum hose at the distributor, will do so. Location is Leeton NSW Trev. also turns out I need a bottom end the Gudgeon pin in one of the cylinders has got sloppy and is quietly and randomly tapping away, thought it was clearances and after the mechanic did them he heard the noise I had been talking about. basically it is pinging 0 to 10 degrees, less at 0 so it sounds like if 0 is good for 91 I have shit fuel ?

Thank you for your help so far I really appreciate it