Rather than using cone filters and other comparable intakes, I have began prototyping this velocity stack. There is said to be advantages in the way the air is introduced into the carburetor via velocity stacks. The idea is that the air is allowed to gradually curve and flow into the carb. With other methods, the air abruptly gets sucked into the intake with added turbulence. This turbulence can cause your fuel and air mixture to be inconsistent.
This is designed around a 54mm intake port for a Honda CB750.
Print with .2mm or better layer height. I used .1mm. 10-15% infill. Print with opening or flare facing down.