MGL Avionics User Forum

I am having a problem with a new installation.
Fuel is AV GAS with 40:1 2 stroke oil, gravity plus 2 fuel pumps. Sensor orientation is as shown in the manual.
During testing (output into a bottle) this worked fine with just gravity feeding and with the pumps running.
However once the engine is running no reading and on investigation the impeller is not rotating.
Cleaning it again allows the test to run with no problem, but run the engine and it stops again !
Trying the test set up again it won’t rotate until cleaned - then repeat it’s ok until engine runs - I have repeated this 3 times now ….
Any ideas ?

The manual shows a slightly different impeller- mine has completely enclosed magnets - does the longer shaft point away from the Hall effect pickup ?


Thanks !

Neil

The magnets appear enclosed from one side only. The exposed side of the magnets must face the sensor located in the main body (so distance between magnets and sensor is very small).

If the sensor stops rotating with the engine running you likely have back pressure wave - but since you state is is a gravity feed system - no pumps running - it is difficult to see what is causing this.
Since there is no pump I am assuming it is a simple carburetor system with a float controlled needle valve ?

Mount the sensor on its side with the arrow on top of the sensor. This way the impeller sapphire spindle tip rests only on one sapphire bearing cup and has virtually zero friction - the impeller will spin with the lightest of flow. If you mount with the arrow on the side the spindle shaft rests on both bearing cups and friction is a lot higher.

Hi Rainer, system is gravity plus 2 pumps just after the outlet of the tank.
It may be a back pressure problem as you say.
It’s a 3 cylinder 2-stroke with 3 carbs.
No exposed magnets on my sender - completely encapsulated, but they are mounted so they are very close to the sensor.
It is mounted in the way you suggest already.


Just tried it “upside down” with the arrow on the bottom and seems to work …
Will see how it goes