'67 650SS Carburettors

Hello again Leonard - From 1962 until 1967 all the 650SS's had 1 1/16 inch Amal monobloc carbs but because the head already had 1 1/8 ports (same as the Atlas) they used those tin sleeves to stop any step and keep a smooth run to the inlet valve.  Obviously the sleeve went through the manifold stub as well. When they introduced the Concentric carbs in 1967 the usual size was 30mm which is almost the same as the port size.  Of course that meant removing the tin sleeves.  They also reduced the thickness of the stub spacer somewhat from 1 inch to about 0.75 inch.  It is possible that you have a very rare bike produced at the cusp of these changes in which you kept the earlier arrangement and just had the 26mm Concentrics in place of the Monoblocs.  There is nothing at wrong with your set-up and unless you are doing lots of high speed runs on track days and the like I'd leave it unless they are very worn.  The fastest 650SS is without doubt the first version made in Birmingham and yours could be a tribute to that..........Have you also got a Competition mag fitted ?  Good luck, Howard   

One observation - the slots at the bottom of the sleeves must be to match up with the rubber balance tube between the spacers.  You don't seem to have that tube, since there are no visible holes.  It's U-shaped, and fits on little spigots under the spacers.

I acquired a ‘68 Atlas last year which came with a single 930 Concentric. For the  type of riding  I do, cross country commuting during the summer and club runs it’s perfect. Starts easy, reliable tick over and no worries about having to keep in tune like a twin setup.  So it’s really down to how you are going to use it and / or whether or not your worried about originality as I’m sure there can’t be that much difference in performance 

hope this helps 

simon 

On my 1965 650SS, I replaced my (worn) concentrics with Amal Premiers, fitted a Pazon electronic ignition with Iridium spark plugs and a modern solid state encapsulated regulator/rectifier. I took a video, which is too large to post, but it shows me starting the bike from stone cold with one kick then opening the choke slides and the bike ticks over immediately. With modern components, twin carbs ARE viable :-)

Kevin