fuel sensor question

[HansLab]

Hi, I need advise, hopefully you can help me out:
yesterday I fulfilled the fuel tests. I have only one tank. All went reasonable (apart from one thing, but I have to sort things out - I might come back to this, later), but:
In the header tank (molded type, behind pass. seat) is a low-fuel sensor (Kitfox-type, black, per manual).
With some 10 liters fuel in the main tank there keeps some 6-10 mm air in the header tank. Result of this is, that the low-fuel sensor is not fully 'under water', and thus the low-fuel light blickers on & off with movements of the plane...
The vent line had some 20cm of fuel in it.

What can I do?
Any advise will be highly appreciated!!

[War Eagle]

What kind of sensor do you have installed in the header tank?

If it is optical I have heard some people have improved the performance by painting the tank black so no outside light gets in.

If it is a float type make sure the float mechanism is not installed upside down.

If you have a return fuel line going to the tank make sure that the return flow doesn't cause any turbulence in the area of the sensor.

[HighWing]

Hans,
First, I have to say I really like your paint scheme and the colors - very nice.

Do you have the header tank from Kitfox - the poly one? If so, mine has the tank inlets on top and the vent outlet is on top as well? With this configuration, It seems that there shouldn't be much residual air in the header tank. My recollection is that some tanks had inlets on top and the vent outlet on the side. Is that your tank configuration? If so, the only way I can think of to purge the air is to totally drain both wing tanks, then fill only one tank. The fuel should purge the air and force it up the empty tank hose. Wait until both tanks have leveled at 6 gallons which should result in all air purged from the header tank and both feeder hoses.

Again, great looking airplane.

[HansLab]

Lowell, WarEagle, glad you thought along! My tank is the Poly molded (new) one, with the inlets on top. The sensor is of a floating type. It is not installed upside down, and I don't have a fuelreturn line (and thus no turbulence).
IMO the sensor works well enough, but the fuel level is just a bit short die to the tiny bit of air in it..

I have only one wingtank, so that eases some things (no equalisation issues to be expected), but I'll take your advise and drain the tank and fill it up again. In this configuration there shouldn't be any air in the header, I agree.
However, I did take the ventline off, and fuel was actually floating over the top of the header: so more fuel would cause the ventline to fill with it - nevertheless there still is some air in the header....

What could be the cause of it, one wanders?