Question: The spray bar in my carburetor appears to rotate when I rotate the throttle barrel or needle valve. Does this matter? I also notice that the spray bar has a groove with some holes in the groove. The groove itself appears to line up with the bottom of the fuel inlet nipple. Do the holes in the groove have to line up with the bottom of the fuel inlet nipple or anything else?

Answer: Rotation of the Spray bar is fine. The holes in the groove do not need to line up with anything. Fuel flows from your tank into the fuel inlet nipple, down the nipple into the carb where it flows into the groove and from there the fuel flows through the holes in the groove and into the spray bar inlet. The groove and two holes in the groove ensures that fuel can flow into the spray bar inlet regardless of orientation of the holes relative to the fuel nipple and allows the throttle barrel to rotate and thereby expanding or restricting the volume of air into the engine.

The needle valve controls the amount of fuel that flows from the exit end of the spray bar into the carburetor throat. It is the mixing ratio of fuel to air that determines how lean or rich the engine runs. When the needle valve is turned in (clockwise) the needle restricts the fuel flowing out of the end of the spray bar and the engine runs lean (less fuel relative to the volume of air). When the needle valve is turned out more (counterclockwise) the fuel flows more plentifully and the engine runs richer (more fuel relative to the volume of air).