OK, whats this one?
Photo date mid-1920s.
My first thought was BSA, but its not, its been suggested Rover,I'm not so sure
Druid forks don't suit BSA/Rover /Triumph
Mag is behind engine, chain cum belt drive, I cannot make out a front brake drum or rim
Some letters can be discerned on the crank case, now photo has been cleaned up it could be Rover at a pinch.
I don't place much reliance on the shape of the tank badge as its similar to many others of the era.
Its got electric light, which must be aftermarket stuff.
The shape of the barrel finning is really bugging me as I think I recognise it but can't remember.
Looks as if its a 500cc or up