These MK1 Concentrics have one advantage: They are the smallest carbs, re venturi diameter. Especially for
Norvins, where you cannot fit any other carb without cutting parts of the frame or rear head fins, if you want
to have your front carb sitting vertically and not touching anywhere else.
Only a week ago, I had a Mikuni flat slide carb on loan from TOPHAM Mikuni with a 32mm dia., to suit my inlets. - No chance. There are pics of a very nice NORVIN somewhere in this forum which will be offered in
an auction somewhen next year. This one does have the Mikuni TM carbs, even with air filters.
Regrettably, it cannot be seen, how the builder got them in place.
Also my experience: Very difficult to adjust MK1 Concentrics. It helps, to have vacuum dials for adjustment.
I found out, that the smoothest tick-over was achieved with a different slide position of front and rear carb,
which is probably caused by the angled centreline of the front inlet channel, if yr carb sits correctly with
unaltered frame and uncut head fins.
Moreover, they use to loosen their adjustment during a ride. They say, that the old ones with pilot jets are
better, than the later ones without.
It must be said, however, that Vince Lonsdale´s "D" runs absolutely perfect on these carbs. It can be done!