Polini Big Valve 50cc Minarelli Vertical kit b.10mm Cylinder

Cylinder kit with Ø40 mm cast iron cylinder and piston with 10 mm gudgeon pin Polini Big Valve 50cc for Minarelli Vertical engines.

The most interesting part of this kit is the Big Valve intake integrated into the cylinder. It uses a 4-petal reed box that allows the engine to draw in the mixture more easily, especially when it starts operating at high RPM.

Polini also works on the internal ducts to better direct the mixture towards the transfers. This helps achieve better cylinder filling, more response when opening the throttle, and a higher top speed, while maintaining the 50cc displacement.

The cylinder is made of cast iron and uses a two-ring piston. The kit also includes a cylinder head, reed box, intake gaskets, and 360° adjustable intake manifold, making it easier to position the carburettor according to the installation.

Polini recommends working with a Squish of 0.8-0.9 mm, keeping the original ignition timing, and using an NGK Spark plug with heat range 9. As a baseline for carburetion, it proposes a Polini CP 19 with original airbox.

Technical specifications

• Manufacturer: Polini.
• Range: Big Valve.
• Reference: 166.0118/10.
• Engine: Minarelli Vertical 2-Stroke.
• Displacement: 50cc.
• Diameter: 40 mm.
• Stroke: 39.2 mm.
• Connecting rod: 80 mm.
• Gudgeon pin: 10 mm.
• Cylinder material: cast iron.
• Piston: 2 rings.
• Intake: 4-petal Big Valve.
• Manifold: 360° adjustable.
• Recommended Squish: 0.8-0.9 mm.
• Timing: original.
• Spark plug: NGK heat range 9.

Recommended carburetion setting

• Carburettor: Polini CP 19.
• Filter: original airbox.
• Main jet: 90.
• Idle jet: 40.
• Valve: Ø25/30.
• Needle: 14/22 - 2nd notch.
• Atomiser: 2.7.
• Float: 5 g.

Applications

MBK

• Booster 50 2-Stroke
• Stunt 50 2-Stroke

YAMAHA

• BW's 50 2-Stroke
• Slider 50 2-Stroke

Important: the carburetion indicated by Polini is a starting point for its recommended setup. If the exhaust, filter, or carburettor is changed, it will be necessary to readjust the mixture.