That is often called the cold start valve or enrichment valve. Put penetrating oil on the connections particularly where the fuel tube goes into the tubing nut and give it time to work. WD40 is not the choice for this, use a penetrating oil.

Looking at it from where the tube goes in, the nut with the tube in it turns CCW (normal, not reverse threads) to loosen, the nut closest to the valve doesn't turn it is held in position with a wrench while another wrench turns the tubing nut. These connections can be seized and hard to break loose, be patient. A tubing wrench should be used on the tubing nut to prevent rounding the edges.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer