Hi Pete, With the butterflies closed there is still a small gap in the venturi, from the factory they painted the clearance with Glyptol (or equivalent) of course putting an antisieze on the butterfly itself, ensuring a leakproof seal, and eliminating the extra air to maintain a proper A/F ratio from the center (primary) carb. If you look at a stock, untouched J2 or other tri-power from the '50s or '60s you will see this. The end (secondary) carbs didn't have a idle system at all. It seems like a lot of trouble for such a small clearance, but hey, they have an extensive engineering budget, so I will go with them.
