It's not the petrol that's changed - it's the oil. Modern synthetic 2 stroke oils are ok at 50:1, whatever the engine manufacturer recommended way back when.
I use 50:1 in my ancient flymo (recommended 16:1). It runs better, almost NO smoke, and doesn't foul plugs anymore.
phil_saunders(a)bigfoot.com
Phil Saunders
September 2009
howtomendit.com for free repair help, information and advice.
