because each circuit is separate, high speed doesn't move your low speed. Reds recently went back to a short needle, before about 10 years ago the most common was a short needle. With a short needle Warm up set high, set low, set idle and go. With a long you set high speed basically blind or off a known setting, warm up , set low speed for idle, set high speed and then come back and set low speed. With a long lS if Initial high speed isn't close from the start you end up chasing it around because Everytime you touch the hight speed the low speed moves and even with the .5 idle Gap you can end up skinny on top fat on the bottom really easily, or skinny bottom with a slightly erratic idle and rich on top. I've seen a lot of blown engines this way , or preventable flames especially when the weather changes and you are trying to stay right on that perfect race tune going into a main.

Advantages of the long is you can get a smoother mid because the low speed stays in play for most of the throttle pull the taper of the needle dictates your mid more then the airway bar adjustment(mid) so you can get a crisper powerband.

With a short you can go in blind set high and low independently and mid only slightly effects low of needed . So you don't have to mess with two needles day to day.

Just my opinion, when I first got into nitro years ago we didn't have long needle carbs and I felt tuning was easier day to day.
​​​​​​

Thanks for all sharing I got into nitro 2 years ago and I'm trying so hard to learn how to tune. I mad sure to use only os motors Nd 21j carb so it would be easier please keep sharing Ur knowledge!!! I HATE ASKING PEOPLE TO HELP ME TUNE MY. MOTOR! Cause people are trying to get ready for Thier mains and cause I'm not the greatest driver I'm not really a priority

You shouldn't have to hate asking man. This hobby does not grow with out shared knowledge