As I flicked through the latest copy of the Star magazine that dropped through my letter box this morning, it felt as though someone had walked over my grave when I spotted the disassembled remains of the manifold that I had made many years ago to marry a SU carburettor to a BSA Rocket 3.
The story began in the early to mid 80's when a certain Mr Pratt brought his Rocket 3 to my house for safe storage while he jaunted off somewhere at the behest of the British army. I can't remember exactly where, but it could have been the Falkland islands. Anyway, whilst the Rocket 3 was in my care he wanted me to remove the oil feeds from the main bearing caps and blank them off, a popular modification I understand, as he was fearful the bleeding of oil pressure from the main bearings would compromise their longevity. When the task was complete apart from reattaching the Amal carbs I began to eye up the possibility of fitting a single SU in their place. I had already carried out a similar modification to my Norton 99 Dominator and it had proved to be very successful, with much improved low down torque and better fuel economy. The Dominator was a much simpler modification to achieve, as it just meant making a flange to suit the SU and welding it onto a standard Norton manifold, the Rocket 3 would present a far bigger challenge.
At the time I was working at an engineering company which had large stocks of various pipe fittings and connectors, so I started weighing up whether any of the fittings could be utilised in the making of a manifold that would fit in the confined space behind the cylinders of a Rocket 3. I think the fittings that I came up with were 3/4" BSP elbows and a 4 way connector, all of which had internal threads. After grinding out the threads and cleaning up the internal surfaces they were brazed onto home made steel flanges, three for the head and one for the SU Carb and I elected to connect the elbows to the 4 way by way of rubber hoses out of expediency. Although I had spent many hours tuning the SU carb for the Dominator I simply removed it and fitted it with the fabricated manifold to the Rocket 3 and was amazed to find that it fired up first kick. Although not perfect, it ran remarkably well with little loss of power and much much improved fuel economy. As I had accurate records of the work that I had done to the SU needle, tuning it for the Dominator I simply bought another SU from the local scrap yard from a mini I think, and modified that one to suit.
I ran the Rocket 3 for a while with the SU in its Dominator tuned state, until Mr Pratt came back off his travels (I think he still owes me for the work) and he took the bike complete with the SU. The next thing I heard was that he had sold the bike to another club member, Tom Kerr who fantasised about fitting carbs off a XS750 or something to the Rocket 3, in any case the SU was removed and I believed then sold/exchanged/gifted to Brian Pollitt complete with manifold. Brian, as his story says, further refined and tuned it to its maximum potential.
Jim Brierley
