I have just bought a Kitfox 4 with a 912 Rotax.Have not flown it yet.Previous owner had problems with fuel coming out the overflow vents and engine running rough.Things that he tried were ,installed fuel return line to bottom of header tank.Installed new mechanical fuel pump,installed an electric fuel pump,installed new carbs.
Anyway the engine still overflows fuel out the carbs at idle .But the interestingly I found out by mistake[forgot to turn fuel on ] is that with the fuel shut OFF she purrs like a kitten from idle to full power and everywhere in between and with the carbmate on it both carbs are in sync at idle ,mid range [3000 rpm] and full power. Also no overflow from carb vents.Now it should not even be running let alone purring like a kitten with the fuel shut off. I pulled the fuel line after the shut off valve and verified that it works and it does turn the fuel flow completely OFF.
I checked the plumbing to and from the header tank to see if it was right and it is .From the header it comes into the cabin to fuel shut off valve then to new electric fuel pump,then to gaslater then to new mechanical fuel pump,then to a T that goes to the fuel return and to another T to the carbs.
The only way I can see that it could be getting fuel [WHEN THE VALVE IS OFF] is from the return line.
It is plumbed at the bottom of the header tank and is then goes to a T between the 2 carbs in the engine compartment.So it must be gravity feeding from the bottom of the header tank.
So i'm wondering if this is causing the problem of the fuel coming out of the overflow on the carbs.Instead of returning excess fuel to the header tank it is gravity feeding more fuel to the carbs when the main fuel it turned on .So I wonder if I could connect the return line somewhere else so that it retuns excess fuel rather then feeding fuel to the carbs?
It has the newer aluminium header tank on it.It just doesn't seem right to me to have the return line going to the BOTTOM of the header tank?
Any help would be greatly appreciated.
THANKS