[xlr8or]

Chappy is right.

The vent whistles are plastic breather tubes that vent the float bowl so the air has somewhere to go as the fuel level changes.
The extensions work best in the secondary side of the carb as the fuel sloshes to the rear of the carb the jet can become exposed on the metering block. The extensions simply extend the opening on the jet to the rear of the bowl.
You might also want to check the floats to make sure they move freely and don't hang up if held at an odd angle to simulate cornering/sloshing forces on them.