Datsun Roadster Forum-311s.org

Noticed when my car is idling the fuel filter has barely any fuel in it. I can see it rhythmically squirt streams of gas into filters and then pause and then continue again, but never filling to even 25% of filter body. When revisiting after parking the car for hours the filter is nearly full. Is this normal or is their an intermittent inop condition? Filter is low to nearly empty when returning from driving. It fills with the engine off later or by next day.

The car idles fine while fuel level is that low (as pictured).

Stock R16 SU’s and appears to be newish stock fuel pump

I have exact same filter and the same operating characteristics. Small in-flow from fuel pump while running but idles fine. Having extra fuel in the filter for next start-up stands to reason....just my 2cents

A "full" fuel filter needs to be changed as its dirty. The filter "fuel Level" increases as it gets more and more plugged on the wetted service.

Also depends on the orientation of the filter -- above or below tank level, fuel suctioned or gravity fed -- and orientation of filter inlet and outlet.

A low filter inlet/high outlet allows captive air to escape, forced out by fuel flow, maximizes wetted filter surface.

As filter is mounted closer to horizontal, higher inlet/lower outlet, keeps more air captive, unless and until jostled out by fuel flow and vibration, less wetted surface.

I use a secondary filter ahead of the Solexes to visually monitor state of prime and inline electric fuel pump output and stalling at 3.5 psi. The Carter rotary electric pump has a metal canister fuel filter ahead of the pump input.

If you are concerned about the volume of fuel, you might try seeing if the fuel return line (after the carbs) is kicking any fuel back to the tank. As long as the float bowls are full (and needle valves closed, which will send excess fuel back to the tank) you are pumping enough fuel.

Thanks for the replies. Yes, Phil I have observed needing to clean my fuel tank. Getting brownish colored grit in the filter from time to time, with one episode making car cutoff and not start. I pulled the filter, tapped it on ground to dislodge sediment and emptied out of filter ends, reinstalled and was able to get home. I now keep a spare filter in trunk.

Odd as picture shows, filter is not heavily dirty, like others I have pulled. I will replace and see if there is trash not visible while installed in system.

Here is how one looked when first ID’d the issue.


Filter is oriented higher than tank and more of a semi-vertical position re. other poster’s response.

I'd check the line from tank by pulling it off from carb into a gal jug crank and see if it pumps well ,also try a vacuum pump from the tank it should pull fuel easy
What yr 311?

Mine has always been like that... half to 3/4 full

Thanks for suggestions redroaster68. I’ll look into those items. Year of 1600 is ‘67.5