Flygas makes a large balance tube kit for believers in this mod, which comes with their manifolds that are made for this purpose. Not something I would do, but the kit looks sanitary, and they claim you can also fly on one carburetor at down to 50% power if one cable breaks (rather than having to go to full power or shut down).
The inertia of fuel in the intake runner has not been mentioned here. The way I understand it, within the mixture of fuel and air the atomized fuel has more mass than the air. More mass equals more inertia, so the fuel tends to go straight past the first turn rather than following the air flow down into the closest cylinder to the carb. This tends to make the further cylinders richer under certain conditions. Manifolds are designed to counter this tendency, and I would be curious how adding a larger balance tube affects this. Intuitively, it would seem a bigger cross tube could change the manifolds flow pattern. It would be interesting to know if the mixture balance between cylinders gets better or worse. This is purely academic for me… I fly an injected Rotax.
