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Predator 212 jetting basics

A stock 212 runs fine on its stock jet. Add an open air filter or a header and it runs lean — that is when the jet kit comes in.

Signs of a lean engine

Bogs when the throttle snaps open.
Surges at part throttle.
Runs better with a little choke.
White spark plug insulator.

Step through sizes

Start one or two sizes above stock and go up one size at a time. Ride, then read the plug: light tan is right, black and sooty is rich, white is lean.

What else matters

The emulsion tube in the kit controls mid-range fuel. Altitude and temperature shift the right size — a jet that is right at sea level is rich in the mountains.