For the most part I have always run a #2 needle and it has worked well for me. Originally my induction system was pretty much stock except for a larger air filter than the Sonex one. I got the #2 dialed in and the engine was happy.
Along the way, I’ve made some induction mods. The big one was fresh air induction, and then I incorporated a pair of nicely ported & polished Great Plains intakes. These mods gave me about a 200 RPM gain, however at WOT in the winter I would tend to go well over the 1400F EGT redline, even at full rich. And it was too rich on the bottom end. I did try a #2.5 needle for a while, but again had the bottom end too rich. So, I decided to try and modify my needle. I bought 3 extras in case it was a disaster.
My thought was to taper the needle a bit more starting when I was within 1/8" of WOT. And I decided I’d like the change in the fuel exit area to be equivalent to 1/4 turn of the needle adjustment. Not a scientific first shot, but it gave me something. This calculated out to the needle being about 0.008" skinnier at WOT.
In this picture you can see I’ve marked the WOT spot, and measured it. There is a piece of scrap clamped onto the needle 1/8" back from WOT. With this setup I used the angle sander with fine paper and would sand and check. The pen is pointing to the WOT spot of the needle.
When I was done, here is the Aeroinjector 1/8" from WOT. This is basically how far I have to pull the throttle back to get to the original needle profile. You can only see the 1/8" back mark because the WOT mark is in the fuel orifice.
WOT - note you can see both blue marks. There is more fuel orifice area due to the 0.008" skinnier needle at that point.
The high EGTs were a problem in the winter. So far I’ve only tested it at about 40F I think - but I have to lean the mixture a little for optimum temps and power. In the summer it’s no problem due to the higher density altitude. I’m pretty happy with this mod. Really no extra tweaking since I’ve put it back together.