To provide a flow control valve for a carburetor, wherein adjustment with the rotation of an adjusting bolt freely by an engine operator is inhibited.

A head 5 of the adjusting bolt 31 is provided with a spline shaft part 5a and a tool receiving groove 6. A turn preventing structure 7 having a turn preventing member 7a, a spline hole 7b, a tool receiving hole 8 and a holding part 7c is held on a pump cover 28 via the holding part 7c. The turn preventing structure 7 is opposed to the head 5 of the adjusting bolt 31, and a flow rate is controlled via the tool receiving hole 8 and the tool receiving groove 6 by using an adjusting tool. After adjustment, the turn preventing structure 7 is thrust to be separated from a pump cover body 28 and it is spline-fitted to the head 5 of the adjusting bolt 31 for impossible adjustment.