Thread: fuel in the air filter

Two or three time I forgot to switch off the fuel selector and my fuel tank would enpty on the floor through the air filter dripping alongside the firewall. That started when I took delivery of the plane in 2007 and has never stopped. Carb inspection by rotax did not show anything wrong. Each time I fly I got that fuel semll in the cabin for a long time. I could not figure out yet if the same leak occurs while flying or only on the ground when I forget to shut of the fuel valve

I am not an expert, but since these are carbureted engines, the needle valve in the float chamber may be leaking. I think that would explain the fuel coming out near the air filter. Can you look inside the flexible air tubing and see if the fuel is in there, too? That would be the path it would take to the air filter from the carb. Of course, getting the carb inspected by Rotax should have picked something like that up unless they only did a visual inspection, then I am not so sure. I have never had a Bing carburetor apart, but I don't think you can look at the needle valve and tell if it has sufficient loading to stop the fuel (under pressure) from leaking. I would think you would need a pressure test of the needle valve. Does your engine run rich with lots of soot? I think that is one of the other effects of a leaky needle valve. Then again, I don't know the effects of the altitude compensation apparatus, either. I have left my fuel valve on by accident in the past and I was worried I would find my fuel on the hangar floor, but it sounds like I was lucky.

I agree the needle valve in at least 1 carb must be laking or the float level is not right. The vent line passes therough the airbox from carb to carb this is most likely where the fuel is coming from. You might want to disconnect the float bowl vent from one or both of the carbs and see if you can find which one is leaking

The needle valve in the float chamber may be leaking. I think that would explain the fuel coming out near the air filter. That would be the path it would take to the air filter from the carb. Of course, getting the carb inspected by Rotax should have picked something like that up unless they only did a visual inspection. It is really amazing and outstanding.