Speed - improved from the stock carb by having a spring loaded float valve but still is lacking a low speed circuit (idle jet + air screw) and different needles are not available (increase the slide cutaway to 2.25mm and set the clip to the 3rd (middle) position. Main jet size needs to be #70 Dellorto jet.)
Dellorto SHA - other than changing the main jet this carb is non-adjustable
BBR Tuning 2-Stroke 66/80cc High-Performance Carburetor - just a clone of the Dellorto SHA carb
Keihin Carburetor Clone - clone of Keihin PTF 16mm. If jets are available then this might be good. Intake bolts onto intake.
Dellorto PHBG 17.5 - good choice. Clamp on size is 24.5mm. Comes with #55 idle jet, #82 main jet, 3mm cutaway, W6 needle, 2.62mm needle jet (increase cutaway 1mm and change idle jet to #40)
Mikuni VM18 - good choice. Clamp on size is 25.7mm. Comes with #30 idle jet, #80 main jet, 1.5mm cutaway, 4F18 needle, O-0 needle jet (increase cutaway to 2.25mm and change idle jet to #25)
Mikuni VM16 - discontinued by Mikuni and hard to find