The BN34/107 is a clear check valve (often referred to as a "teardrop"-style check valve) used in Mikuni Super BN-series carburetors. It ensures proper one-way fuel flow within the pump assembly.

These check valves are generally used to help regulate pump operation by preventing fuel backflow when the pump chamber resets.

Need two per carb? Likely yes—most BN-series carbs use a pair of check valves, similar to BN34/124. However, confirm with your model’s parts diagram for precision.