Fuel Filter

[Bar Vitelli]

I’ve had a fuel issue on two of my cars, changed the tank on one of them, new pump, new rod, new pipes, new spacer, new gaskets, new filter, still did not work. Put the filter on the wrong way round (with the arrow pointing to carb in the other direction) and it works a treat! Can anyone explain why? It’s driving me crazy. Did the same with the fuel filter on the other car as well and it fixed it.

[ChrisRLewis]

That's a strange one. Do you have the fuel filter fitted before or after the fuel pump?

[Bar Vitelli]

Before the fuel pump. I’ve just watched a youtube video that says it should not make a difference to it working. The arrow is to help the filter catch and show the debris so you know when to change it. But, both times we had a virtually empty filter which when we turned it around was then full of fuel. They are top quality filters bought from Ricambio.

[Minijohn]

Maybe there's some sort of one-way valve in the filter that's been assembled incorrectly.
I'd take one off & try blowing through it in each direction.

[Bar Vitelli]

Thanks, John, I’ve tried that and it blows both ways. I should not complian really as it’s working, I’m just at a loss to explain it and have lost weeks on it!

[Abarth982]

I like a puzzle but this one has got me baffled ...
I wonder if the filter does flow very slightly differently depending on which way it's fitted and the tank is creating a vacuum that the pump can't overcome one way around.  I guess if you took the fuel cap off with the filter fitted the correct way and it still doesn't flow that would eliminate that theory!
I also wondered if the carb/engine was creating a vacuum that the pump couldn't overcome but I just can't see how that could be.
Last thought was if the pump (for some reason, worn cam lobe (if that's what if works off)) is marginal and will only pump sufficiently with the filter one way around.  What would be interesting would be to bypass the fuel pump with a little electric one and see if that makes a difference.
Clean out of ideas now 

[Bar Vitelli]

I’ve got a sinking feeling that my mechanic may have tightened the jubilee clips at each end of the fuel filter too tightly. Reversing the fuel filter might not be the issue, if the clips have gone back on not as tight that would help explain the dramatic difference between a virtually empty fuel filter and a full one.  It’s such a simple explanation I feel stupid for missing it but Fiat’s have a habit of catching you out in this way!

[Macmonkey]

I must admit that I have made that very mistake myself! I now use a fuel filter that is glass in the middle and the two ends are metal, the filter inside can be easily removed and cleaned as necessary. It was only about £8 which isn't much more that a plastic filter and the added bonus is that it isn't likely to melt at any point.