Information please: My 1950 8N carb has a small tapped hole in the casting just forward of the drain. In the manual's exploded view it is shown as: Ref. No. 7, Drill plug, nozzle hole (No. 8-32), Marvel-Schebler Part Number 15-409. What is the purpose/function of this little thig-a-ma-jig? Thanks for any info.