I haven't purchased them yet. How do you remove the tiny screw? What are the other tubes below?
The "tubes below" are used for barrel to barrel balance measurement. The tool used is a manometer or vacuum gauge. Most motorcycle shops have these ... trade named "Carb Stix". They use a group of capillary tubes partially filled with mercury with hoses fastened to the tubes. The hoses go onto your carb tubes (measuring manifold vacuum). If you loosen the tubes (they are threaded) off their seats, you'll be able to measure manifold vacuum of each throat of the intake. The air/bypass screws (in the recessed wells next to the "tubes below") can be adjusted to balance the carb throats. Carb Stix and multi vacuum gauge setups are still available. Nowadays ... a snail type gauge measuring the air flow at the top of the carb gives you the same tuning / balancing / linkage adjustment result. The air/bypass screws are normally seated (gently) closed, but can be used for fine adjustment (as long as you're not compensating for another problem with the carb).
