[D13]

Mechanical fuel pumps do not like restrictions before them, they push better than they suck. The opuropse of the filter is to protect the carb / injectors, including from debris of a pump failure. It should always be after the pump. It's ok to protect the pump with a low restriction high flow filter, although this is pretty much a waste on most mechanical pumps. They will happliy pump fine sand with no real issues.

As an example, the big failure on 6.2 diesel electric lift pumps is large tank debris ingested by the pump, either just small enough to pass the sock or due to sock failure. The cure is a 60 micron filter right before the pump, and retaining the sub-20 micron filter to protect the expensive injection pump. That way the lift pump is protected but doesn't have to suck fuel very far, and the injection pump and injectors are protected with little pressure drop.