I use Castrol Valvemaster Classic in mine (lead replacement & octane booster) with Super Unleaded (97/98 RON). On 95 RON, it runs like carp, with the mixture (generous on the additive), it goes like s**t off a shovel. The only slight loss of power and pinking I get is usually up one of the Yorks Moors hills with a headwind and a slightly optimistic rider with a twisty right hand. I've just managed to get 3 bottles of the Castrol off Fleabay for the equivalent of £11.50 each (cheapest I could get it). If they introduce gnat's p**s petrol, I'll just whack more in or get the rocket fuel mentioned elsewhere.