I have not tested the optional needles as of yet. I am awaiting their release from Orion.

I expect that their purpose is to allow the ability to move the adj. range of the low speed needle around, due to the different dia. and taper angles of the optional needles. I think this is a really great idea and it will surely be nice to have this option to change the behavior of the low speed mixture.

Motorcycle carbs have the same adj. ability and it has always been crucial to have this adj. available.

The LSN actually has 2 functions. It controls the idle mixture (obviously) by controlling the taper position in relation to the spray nozzle. But the second function of the LSN is to control the relationship of fuel entering the venturi as the slide is lifted off it's seat. So the taper of the needle controls the mixture from 1/16 - 1/3 throttle approximately. This is the throttle opening area that is altered to adjust throttle response, and it can be very effective in tuning for top performance.

BK