why 34s??

Why 34 flatties and not 36 or 38s?

more responsive on small to medium sized motors on the street;)

Exactly. I believe ELR's came with 34mm flatslides. Big honking carbs for drag racing (38'-40s), smaller carbs for road racing (34's) and smaller yet for choked off by emission controls streetbikes(28-32's).

I have 36mm flatslides on an 1170 GPz and I find it very responsive. A friend took it for a ride and was very surprised how tractable and easy it is to ride. I had trouble getting it too idle smoothly, stalling at idle until I got used to setting it up.