If you find yourself in North Wales, there's a museum on the A542 out of Llangollen towards the Horseshoe Pass.
This is a privately run affair, and looks like it works pretty much hand to mouth, but even though its a small place I spent an absolute age in there - (early March, bloody freezing in there too!)
A lot of the bikes and cars there are used on the road, I presume the owners allow their bike to be kept as exhibits when not in use.
Also they sell a good few original period spares, and not at silly prices
And if its a cold day, take a jumper
http://www.llangollenmotormuseum.co.uk/