I have a 1961 R27 I just bought receintly.
It starts very hard when cold, usually I have to push it but after it warms up a little, as little as around one block, it starts good.
But when I am riding it and stop it increases in speed when it is idling. It runs down the road great.
I have had the Bing Carb apart two times. Everything looks good the slide spring seems good and the slide works good. I checked the throttle at the grip and it seems to be working good also. The last time I had it apart it put gas in the float bowl to see of the float would float and it seemed to do that also. I don't know these real good but I am learning. Thanks for any help.