One result of my curiosity regarding flat slide, rod metered carburetors is that I found several people in the light sport aircraft crowd who have cracked the mystery of the POSA. For years the homebuilt crowd has used the POSA carburetor with decent results. It seems that part of the reason it acts like a full throttle only race carburetor is the design of the throttle block and the taper of the fuel rod. As one analysis stated it, the carburetor uses linear fuel metering with a non-linear air passage. So the apparent fix was to reshape the rod to reflect a non-linear fuel metering which, by trial and error match the throttle block air passage at idle, mid and high speed operation.
Now that bit of information will have to wait until I actually can get one in my hand. If anything all of this research has made me more curious than ever. But for the future until that does happen I will plan on using the AMAL Mark II. I still want a POSA! At least to experiment with.
A pair of chromed POSA carbs for a Harley.