It depends what Angela is, a four stroke single presumably ("Thumper"), but air or water cooled and Japanese or British/Indian? What grade is recommended? What use is she put to?
The oil manufacturers would have us believe that modern car oils contain an additive that causes clutch slip when used in a motorcycle with shared engine/transmission.
I once made the mistake of putting car oil in a Montesa clutch and it not only slipped but wouldn't free off either. But then Duckhams Q in those days was strange stuff with a colour and smell all of its own so who knows what it was made of.
I've no personal experience but a pal runs old British four strokes in competition and buys the cheapest oil he can get but changes it frequently. I haven't heard from him of any problems over about twenty years or so.
More info required really.
Ref Hinckley, I recall a magazine article yonks ago on one of the original triples that had been run by a dispatcher for about 80,000 miles with no oil changes. They stripped it and measured it and there was no intolerable wear. Can't remember which mag it was but I'd like to get a hold of it now.