The BN34/124 is a clear check valve used in Mikuni Super BN-series round-pump carburetors, such as the BN34, BN38, and BN44. It functions to prevent backflow and ensure smooth, one-way fuel flow within the pump assembly.

In a standard carb rebuild, two check valves are required. Most parts diagrams indicate the BN34/124 check valve as item 3, with a quantity of 2 per carb.