Reece Fish, or Reece Minnow carbs were a special carb made by a small manufacturer in the UK, I have had a couple over the years, but never really tuned one on a car.
They have a butterfly and pendulum style swinging arm that has a hole in one end that passes over a graduated channel that gets wider as you open the throttle.
The carb is completely adjustable via needle valves and the swinging arm, no jets to change! great concept!
I know they were the must have on Mini Se7en racers back in the 850 days, the class was restricted (still is) to a single carby, but eventually half a weber 45 took over!
There was a 1 1/4 and an 1 1/2 versions, but they flow a lot more than an SU, a single 1 1/4 would suit most road cars / small bores and race cars used the 1 1/2 size. I never heard / saw any one need twins!
Dave Vizard explains them in How to modify your mini. A bit dated now, but, every one should have a copy!
