I too like this road, but found it to be quite heavily policed and with a far bit if traffic on the popular days. It is pretty, but watch for the bizzies.
This is great on a BMW-GS or similar.
Follow signs off A44 to NANT-Y-MOCH,its a single track all the way with a lot of cattle grids but the views are stunning at the dam(which you cross) and on the decent into Talybont.There are two pubs at the end if you need to calm your nerves. This has been done often on 'sport bikes'.