Driven Defender and Booster - Lead Replacement Plus Octane Booster - 295ml Bottle. If your Norton (or any other classic motorcycle) has not been fitted with new 'unleaded' type valve seats, then using modern unleaded petrol will lead to excessive wear of your valve seats.
Driven is a well known specialist American oil company, producting oils and additives for the motor racing industry - and one of their products is this fuel additive that protects valve seats on older style 'leaded' engines, as well as increasing octane - just add a small measure of this liquid to your fuel tank each time you fill up and you will effectively be changing your 'unleaded' specification to 'leaded type - and therefore will protect valve seats.
This 295ml/10 Fl oz bottle will treat up to 25 gallons (not litres . . . remember it is a US company!) of fuel. The bottle has graduations along its side, along with a clear plastic area so you can easily see how much additive you are adding on each fill up.
I have recently stocked this item because other UK additives have been getting harder to find - and it is supplied by my main racing fuel distributor, so know they can be trusted. I am using this additive myself now in my roadgoing Vincent and will report back results later in 2018
Always read instructions before use.