could be modern fuel. has it been stood over winter, apparently, modern non premium fules contain less preservatives than they used to and basic petrols contain 5% ethanol.
https://www.nortonownersclub.org/noc...eral/551269389
you can buy fuel preservatives nowadays: eg:
https://www.ebay.co.uk/itm/Bill-Hirs...8AAOSwlp1Z3JTr
nb: i have seen it forsale in tiny bottles: