98 and above octane number [i.e. the Oz RON rating - the US AKI rating is a bit different] fuels are best avoided, for
any carburetted engine.
They are intended for, and best used in, fuel-injected engines with
closed-loop engine management systems. That is, those with both Exhaust Gas Oxygen
and Knock Detector sensors.
Edit: The physical properties of these fuels may differ somewhat from lower-octane fuels; i.e. such things as density, viscosity and surface tension - which all affect the actual air/fuel mixture ratio of a carby. It's a known issue for carburetted motorcycles, but these of course have much higher specific power outputs [i.e. in kW per Litre of engine displacement terms] than OPE engines. These fuels also often contain oxygenated compounds other than ethanol, too
But I'm a believer in avoiding potential problems, and it's no great hassle to buy 95 for the garden machines. My Coleman Dual Fuel pressure lantern seems to run OK on it, too!
Premium 95 is the safest on all fronts, including shelf life, so long as it does
not contain any ethanol. I don't buy petrol from my sole local United servo, for just this reason. While there are Federal 'fuel rules' on marketable fuel standards, in practice enforcement falls to the States. And they are 'toothless tigers' on this issue, particularly as regards labels on pumps stating ethanol content. Or 'biodiesel content', for that matter.
