The o-290, series 1-3, and likely many others, has an accy case gear driven mechanical pump. Also there should be an electric fuel boost pump as a backup, also helps prime etc, although it is not required and many certified piston aircraft have a mechanical fuel pump only.
The RV-4, being a low wing, does not pull from 'both'. For a numbers of reason discussed on the the forums. Its either left or right.
Thanks for the quick reply. Could you direct me to the forum threads that discuss why RV-4's don't feed like a simple C150? Does it have to do with aerobatics or something?
Also, did Van's ever specify a specific fuel pump when used for boost?