Have just uncovered my late husband's BSA Sloper (1931-493cc) in his garage. Started it up no bother, but it's backfiring a bit, and not running smoothly. It starts easily, but when I try to open the air throttle (?) it starts to falter then gradually dies. I got a neighbour who's a bit handy to clean up the carburettor, but this hasn't made much of a difference. He thinks it may be a timing issue, but doesn't know how to adjust it. I obviously know nothing about it myself, but wondered if there is any helpful advice out there about how to fix this? Otherwise it's a lovely bike and in good condition.