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I have just upgraded my fuel filtering system by adding a modern plastic filter in line with the original glass bowl filter. But what I can't quite get my head around is why both of them only seem to be 30-50% full of fuel (when idling).

Assuming they don't "need" to be full, how does the engine "know" how much fuel needs to be / should be in the filter bowls?

It is all in the orientation of the filter. The glass bowl which has the in and out side at the same height it should be full as fuel comes in, goes to the bottom and then back out the top. The inline depends on its orientation - if you had it mounted vertically with in at the bottom then the filter will fill up before fuel can get out to top so would be full all the time. Mine is on its side so the filter only ever half fills as fuel is going out to the engine as fast as it goes in from the pump.

The carb floats allow the right amount of fuel in and as long as the fuel is in the filter so it can get out the outlet then the the engine gets all the fuel it needs.

"Assuming they don't "need" to be full, how does the engine "know" how much fuel needs to be / should be in the filter bowls?" The engine does not need to know other than the fuel pump providing the the right amount of fuel at the right pressure

Julian - try not to over think these things

Garry

As Garry has said ^^ Also if you have a low pressure but high volume electric fuel pump fitted, when the float bowl is full the fuel delivery is stopped by the float valve and you will see the fuel filter fill up then drain as the floats drop and valve open.

I've disconnected the electric pump the PO fitted to Hemi and only use it to prime now, it will be removed when I re-pipe the fuel system.

AustHaflinger wrote: ↑Sat Apr 30, 2022 3:14 am Julian - try not to over think these things

Garry

Julian - if you are worried about it get a fuel filter that is not transparent then you cannot see what is going on inside