If you have 4.5 gallons in one wing and zero in the other, you have a problem that should be addressed before the next flight. As long as the plane is on level ground and the fuel selectors on, there should be almost identical amounts of fuel in the wing tanks, as they are interconnected. The fuel flows freely between the two wings. If one wing has fuel and the other does not, you may not be feeding your header tank from both wings, only one. Therefore, you will have less usable fuel than you think you have and possible have fuel exhaustion if you base your flying time on gallons you "think" you have available. If you do continue to fly before you address this issue, trust your header tank fuel gauge (the bobbing cork) and not the gallons you "think" you have usable.
If you have a strong fuel small in the cockpit, you have a fuel leak. You may be lucky and find it is only a loose connector somewhere on the tubing that carries the fuel from the header tank to the engine, most likely at the base of the tank or at the fuel selectors. Also, if you have a fuel sight gauge to the left of the pilots left thigh which reads the fuel in the wing, check it see if it has a small leak. Rub it with you finger and then sniff your finger. If it smells like avgas, the fuel leak is coming from the gauge. It is a fairly easy fix by replacing the plastic lens using the correct procedure which includes putting gas resistant silent on the threads of the screws that hold the unit together. If you are unlucky, you will have to remove the header tank and have it rebuilt. This is a big job that will cost you around $1000 between removal, repair and replacement. I was once in an airplane that had a fire in the cockpit fueled by a small leak in the fuel system. I will not fly in any airplane that smells from gas. A very small spark from something as simple as keys banging against metal could spark a fire. I was very lucky that my co-pilot was quick and sprayed me and the rest of the interior with a halon fire extinguisher. This put the fire out, I had burns and the plane was seriously damaged. Be careful! Glen Davis CFII Ercoupe N3103H Tiger N70GD Glen Davis 917 297 1111 www.ishootpictures.com www.ercoupepilot.com
