Fuel Filter orientation, gravity, vacuum

[Paul Storaasli]

When installing a fuel filter between the carbs and the petcock, does its orientation and/or the presence of air inside the filter matter?  In the image below, taken from http://www.gstwin.com/carb_work.htm, The fuel filter is almost vertically oriented.  If the fuel is vacuum or gravity fed, I would think it might have some trouble getting into the carbs if there is any air in the filter.  Has anyone had a problem like this?

Thank you.
Paul

[KevinC]

The flow is supposed to go through the filter one way, but other than that it doesn't really matter where you put it. The fuel flow is strictly gravity - vacuum is only used to open the petcock, so that it closes automatically when the engine isn't running.

The carb float bowls are lower than the fuel tank, so the gas will fill them as long as there isn't a point in the tubing that is higher than the bottom of the tank.

I suppose the filter will have more or less trapped air in it, depending on which way it is oriented, but I've never seen this be a problem. I usually put it vertical right after the tank myself, that way it fills nicely.