Trying to fine tune your carburetor after upgrading your air intake and/or exhaust?
Try getting a slightly larger pilot jet to smooth out the revving from 1/4 to 3/4 throttle.
Available in sizes 35 to 45.
The pilot jet controls the volume of fuel delivery in your carburetor from idle to approximately 1/2 throttle, when the main jet takes over.
If you've upgraded your carburetor, air intake, or exhaust, you may find you're running leaner when idling. A larger pilot jet can help restore the correct air/fuel ratio at low speeds.
Most stock 150cc carburetors come with a size 35 pilot jet; most 250cc buggy carbs have a size 38 pilot jet. Pilot jets should be increased in size in single steps: 35 to a 38, 38 to a 40, etc until you reach the correct air/fuel ratio when idling and at full throttle.
Carb tuning tip:
If your carb is backfiring heavy when you let off on the gas after being at wide open throttle, your pilot jet may be too large. If it's lightly popping when revving down, the pilot jet may be too small.
When properly jetted, your motor should rev smoothly up from idle to wide open, and back down.
If your motor is popping or bogging when you're on the throttle, it's usually an incorrect main jet size, dirty carburetor, poor fuel or fuel supply, or incorrectly adjusted valves.