for MINARELLI vertical inner diameter: 25mm with big reed valve Product description Basically, manifolds are responsible for the fl ow of the gas-air mixture to your carburetor. Your original manifold’ s fl ow channel is usually smaller than your carburetor – creating a throttle effect, resulting in a hearty power reduction. A tuning manifold corrects this imbalance with a larger diameter, giving you more fl ow and more power – even with your original carburetor. Installing a tuning carburetor without an open manifold doesn’ t make sense. All open manifolds have two things in common: an optimized diameter as well as a shorter and better induction path. Irregardless which sport manifold you choose, your scooter will reward you with a remarkably higher performance. Get some fresh air in your system! For those who want it big, we recommend the POLINI BIG VALVE. BIG VALVE manifolds are available for 21 – 25mm carburetors. Ideal if you’ ve already built in a larger carburetor or if you