Tamper resistant carburetor mixture needles

A tamper resistant mixture adjustment screw arrangement for a carburetor (20). The arrangement includes a carburetor body (22) having at least one air/fuel adjustment screw (24; 26) threaded therein. The adjustment screw (24; 26) has a threaded shank (28) and a head portion (30). The head portion (30) is defined by a smooth top surface (32) and an undulant, uneven side surface (34) capable of being engaged and mated by an adjusting tool (42) having a complementary undulant, uneven side surface (48) for initially adjusting the air/fuel mixture in the carburetor (20). A blocking curb (38) extends from the carburetor body (22) to a level which at least substantially corresponds to a projecting extent of each adjustment screw (24; 26) and being closely spaced to the screw head (30) to prevent the screw (24; 26) from being turned by commonly available tools, but to permit the screw (24; 26) to be adjusted by the adjusting tool (42).