My favorite upgrades in order:
(1) SBP Expansion Chamber---noticed a huge performance increase for low end torque and acceleration.
(2) Rear Wheel Sprocket Adapter---for the sake of the spokes and peace of mind
(3) Dellorto Clone (RT) Carburetor--- power increase
(4) Wipperman R8 BMX Chain--- super strong small chain that is less bulky and runs through my sprockets smoothly and clears my rear tire better.
(5) Dual Brake Lever--- for simple operation and faster stopping time (for me)
(6) Bottle Boost---waste of money, noticed no difference in performance at all