Genuine Mikuni Pilot Jet – #12.5 and up
30 mm and larger UFO installation requires that you reduce your pilot jet by approximately 1/2 (or 1/2 plus 1) of the size you were using prior to UFO installation. These small pilots are usually not available at your local dealer. List the size you want in the special instruction area during the checkout process. Pilot jets come in increments of 2.5 (15, 17.5, 20, 22.5 etc…).
The Mikuni Pilot Jet System
This system works at or just above engine idle (see diagram). Only a very small amount of vacuum can be created by the engine when it is at idle speed. The Mikuni pilot system is placed nearest the intake manifold (where there is the most suction) because of the limited velocity of air (vacuum) moving through the carb at idle speed. Limited velocity equals limited suction – that’s why the fuel for this circuit needs to be easily drawn from the pilot circuit. The pilot circuit is controlled by means of a pilot outlet and a bypass. At idle, fuel metered by the pilot jet is mixed with air and broken into fine particles of fuel vapor. This is adjusted by the air or fuel screw, which is also sometimes known as the pilot screw. When the throttle is opened slightly, the bypass draws in more fuel in to immediately compensate for the increased airflow. The pilot jet works in coordination with the fuel/air mixture screw also often referred to as the pilot screw. Like the pilot jet, this screw has little to no effect on the fuel/air mixture above idle speeds.
Mikuni Pilot Jet