Hugh,


The Perry carburettor and their pump carburettor (like the Moki carburettor), do not have a "low-speed needle" as such.
They have an 'idle mixture disk', which does the same thing, i.e. meters the fuel mixture at part-throttle settings.

So, if the Perry instructions say; "adjust the idle-mixture disk", it is exactly the same as saying; "adjust the low-speed needle".


And yes, in their instructions Perry often refers to their proprietary carburettors and their means of fuel control.


Besides raising the pump's pressure and throughput, to make the mixture excessively rich at full throttle, the further use of the pump's 'screw' is to control the mixture strength in the mid-range.

If both the high-speed and the low-speed needles are adjusted, and the pump pressure is on the high side; the engine will run quite rich in the mid-range.
You then need to lower the pump's pressure and readjust both needles (open then slightly), in order to achieve a linear fuel curve.