Koso BA003211 Mini 3 Air/Fuel Ratio Gauge: Automotive. Buy Koso BA003211 Mini 3 Air/Fuel Ratio Gauge: Air & Fuel Ratio - ✓ FREE DELIVERY possible on eligible purchases. With backlight 。 Sensor include 。 Fits 4 strokes engines only 。 Easy to install 。 Our new Mini 3 air/fuel ratio gauge was especially designed to help you tune your carbureted or fuel injected engine. This meter can be easily installed on any type of stroke engine by installing the sensor in the exhaust system and connecting the instrument to a 12 v DC source of power. 。 。 。