Standard factory jetting is almost always "lean" to meet emissions standards, which can leave your scooter feeling sluggish. The Prima 4mm Main Jet Kit is the essential tool for riders installing big-bore kits, performance exhausts, or high-flow air filters. With 10 precision-machined sizes, you can eliminate "flat spots" and find the perfect air-fuel ratio for maximum throttle response.
This 4mm kit fits most 50cc to 125cc "retro" and performance scooters using a 139QMB engine or Genuine 2-stroke platforms:
Pro Tuning Tip: Always start with the largest jet first and work your way down. A "rich" mixture (too much fuel) is safe, but a "lean" mixture (too little fuel) can cause your engine to overheat and seize. Look for a "toasted marshmallow" brown color on your spark plug for the perfect tune.
Note: Not compatible with Mikuni or Dellorto carburetors. Please verify that your current jet has an M4 thread before ordering.
Original Parts For Scooters SKU 114-49-10PCS, 114-85-10PCS
