I'll buck the trend here!
Autoglym bike cleaner... bl**dy expensive, but spray it on and go for a cuppa, if it's *really* bad (like my MZ

) then spray another lot on and go for another cuppa.
Then jetwash off with a cheap Karcher.
Works like a charm on mine (or it does when I get round to washing the thing... at least once a year, sometimes even more often than that!)
I always found parrafin not that effective outside of a constant flow, and then it only makes a mess of the drive/me/everything nearby/everythng I touch... most tedious!