If you have a 1275 engine in a Sprite, you should try these needles. It’s hard to show in the video or pictures, but the taper is slightly different than stock, and it just makes your car work better. Case in point—we had a great Bugeye that was not transitioning smoothly in the mid-range. We richened the mixture slightly, which helped, but the idle went away, and got rough. And herein lies the challenge with SU carbs… the mixture setting is a coarse adjustment that might help one part of the RPM range, and hurt another. So the needle profile is a different line of attack, and in the case of this 1275 Bugeye, the #3 needle was the answer. We fit a pair and the car was transformed!
I’ll leave this up to the petri-engineers to explain, but I believe that 10% ethanol in our fuel requires a slightly richer setting than back when the AN needle was specified for these cars when fuel was ethanol-free. Try a pair of #3 needles and see if you agree that this is just what your engine needs to run on modern fuel.