It can be a combination of factors.
This pipe is surely a great pipe - good acceleration and power.
I don't know your exact engine+setup+tuning, however, if you have a non-stock cilinder, like a ported 50cc or even a 70cc, you should surely get the high pressure clutch springs. These will let your clutch generate a higher rpm before pulling off the line.
Also, make sure sure your fuel+air mixture is right. Use a Malossi airfilter and a 13/13 carb to get full potential.