They are power jets for when you're running alcohol. They let more fuel in at wide open throttle. Its basically an extra fuel source.You can adjust how much extra fuel comes in by turning the knob on the power jet. You can run with them all the way open or closed if need be but usually they're open some. They allow for that fine tuning on the fly without opening your carb to change jets. Again, its for wide open throttle only. Hope this helps