The scavenge tube is a SAFETY devise!!! It takes the raw fuel that drips down the updraft carb and routes it to the manifold. This way the fuel does not accumulate and drip out of the carb
~boom.
The tube is just a piece of 1/8 copper tubing usually with compression fittings on both ends. The nuts are 3/8 as I remember and should be snug so they don't leak fuel or air. The extra air is especially bothersome for the carb at low speeds.
Dave Neptune
