Prima Main Jet Tuning Kit (4mm) - 50cc Carburetors

Fine-tune your air-fuel mixture for peak performance with this comprehensive 10-piece jetting kit.

The Prima 4mm Keihin PB Main Jet Kit is the essential tool for riders upgrading their exhaust, air filter, or big-bore kit. These M4-threaded jets are designed for Genuine 50cc 2-stroke scooters and 139QMB 4-stroke engines equipped with CVK or PB-style carburetors. Whether you are correcting a factory-lean condition or tuning for new performance mods, this kit provides the range you need to find the perfect "plug color."

Kit Contents:

Includes one of each of the following 10 sizes:

• #70, #75, #80, #85, #90, #95, #100, #105, #110, and #115

Carburetor Compatibility: Keihin PB Style, CVK Style, and PD18J model carburetors with 4mm main jet ports found on most 50cc carbureted scooters, including the following models.

• Genuine Scooter Co (50cc 2-Stroke): Buddy 50, RoughHouse 50, Rattler 50
• Chicago Scooter Co. (50cc 4-Stroke): Go., Go. Max, Nitro, Bella
• Chinese GY6 50cc (139QMB): TaoTao, Wolf, Ice Bear, Peace Sports, Bintelli, and others utilizing PD18J or CVK-style carburetors.

Technical Specifications:

• Thread Size: M4 x 0.7mm
• Overall Length: 7mm
• Jet Body Diameter: 5mm
• Material: High-Precision Machined Brass
• SKU: 1300-1129
• #70 Jet Inner diameter:  0.70mm (70)
  
• #75 Jet Inner diameter:  0.75mm (75)
• #80 Jet Inner diameter:  0.80mm (80)
• #85 Jet Inner diameter:  0.85mm (85)
• #90 Jet Inner diameter:  0.90mm (90)
• #95 Jet Inner diameter:  0.95mm (95)
• #100 Jet Inner diameter:  1.00mm (100)
• #105 Jet Inner diameter:  1.05mm (105)
• #110 Jet Inner diameter: 1.10mm (110)
• #115 Jet Inner diameter: 1.15mm (115)

?? Tuning Tip: The "Plug Chop" Method: Proper jetting is critical to your engine's health. Always start with a larger jet than you anticipate needing and "jet down" to the correct size. A "lean" condition (too small of a jet) causes excessive heat that can seize your cylinder in seconds.

To find the perfect tune, perform a Plug Chop: Run the scooter at wide-open throttle (WOT) for 15–30 seconds, kill the engine, and inspect the spark plug.

• Coffee Brown: Perfect air-fuel mixture.

• White/Grey: Too lean (Install a larger jet immediately).

• Sooty Black: Too rich (Install a smaller jet).

Original Parts For Scooters SKU 114-49-10PCS, 114-85-10PCS