Tamper resistant idle adjustment screw

In a carburetor for an internal combustion engine, the carburetor having a body through which an air passage extends and an idle speed fuel circuit for supplying fuel to the passage to mix with air and form an air-fuel mixture combusted in the engine, and an idle adjustment screw for adjusting the quantity of fuel mixed with air to make the resultant mixture richer or leaner, the idle adjustment screw being settable during flow testing of the carburetor to an initial adjustment position, the improvement comprising means for making the idle adjustment screw tamper resistant to inhibit further adjustment of the screw after the carburetor is installed on the engine, the carburetor body having a cavity formed for the screw and a bore transverse to the longitudinal axis of the cavity, the tamper resistant means including a plug for sealing the open end of the cavity and a blocking pin inserted into the bore, the location of the bore being such that the blocking pin is between the idle adjustment screw and the plug, the length and diameter of the pin being such as to substantially block the cavity so an adjustment tool cannot be brought to bear on the idle adjustment screw even if the seal formed by the plug is violated and the length of the blocking pin further being such that the blocking pin is captured in the bore by staking or the like and cannot be removed therefrom whereby the tamper resisting means inhibits adjustment of the idle adjustment screw to produce an air-fuel mixture for which relatively higher engine emissions are produced than are produced with the idle adjustment screw set to its initial adjustment.