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James,
1. From what you described, it sounds to me like you had a fuel pump failure, just like you thought.
2. On my 66 Alon, the tip of the nose tank float disappears with about 3 gallons remaining in the nose tank WHEN THE PLANE IS SITTING LEVEL ON THE GROUND. I have no data on this with the plane in level flight, and don't intend to collect any. See the attached Excel spreadsheet. Note that this data is for my plane only, was only checked one time, and may be wrong! Don't bet your life on it.
3. My wing fuel tanks both have a hole drilled through them top to bottom. These holes have a long cotter pin in them. The cotter pin holds a plastic "capplug" in place on the bottom of the cap. This is described in one of the Alon service bulletins. The capplug acts as a baffle to keep an excessive amount of fuel from venting out of the tank when climbing out with full tanks. My tanks do, and always have, vented fuel out of the wing tank caps when the tanks are filled and the plane is climbing at a steep angle. This only happens if the tanks are filled pretty close to full. Usually I just fill the tanks to within an inch of the top, and the venting is minimized or eliminated. Even with the tanks completely full, I doubt that I lose even a gallon of fuel to venting, let alone several gallons. There is just a fine spray of fuel visible while climbing. When I level out, the spray stops. The fuel can only vent out of the tank if the fuel level is up to the cap. If the fuel can't reach the cap, it can't siphon out.
4. You didn't say if you saw fuel siphoning out of your wing tank while the header tank was close to empty or not, however, if you had a failed fuel pump, and if you were in a climb attitude, fuel would flow from the header tank, through the header overflow outlet at the rear of the header tank and back into the wing tanks. With no fuel pump to refill the header tank, you could possibly overflow the header fuel into the wing tanks and have no way of getting it back into the header tank. I suspect that this is what happened to you. If I put my plane in a steep climb at full throttle for an extended period of time, the nose tank float will drop, and the wing tank gauge will show an increase in level from where it was when the climb was started. This is due to the header tank being "tipped back" and the fuel flowing out of the overflow outlet at the rear of the header tank and flowing back into the wing tanks. After leveling out, the fuel pump will pump the fuel back into the header tank so that the header tank is once gain full. My airplane will not maintain a full header tank in a steep climb at full throttle due to this overflowing of fuel back to the wing tanks.
5. The fuel pump restrictor is part of the elbow shaped fitting at the outlet of the fuel pump. On my plane, this is a standard, stock, AN or MS part, not a modified fitting. If my memory serves (doubtful) I think that the hole in it is larger than 1/16th inch, but maybe not as large as 1/8 inch.
6. My fuel tank caps are very tight also, and like you said, they are pretty difficult to remove. I usually put a drop of oil on the rubber gasket, and that makes the easy to remove, but only lasts 2 or 3 flights and then I have to do it again. If the gaskets get completely dry, I sometimes have to resort to using a pair of pliers to turn them.
Hope some of this is of some use to you. Looking forward to seeing you at Rutherford sometime soon. I flew up there today for lunch. The visibility must have been 100 miles and the banana pudding was terrific!
Best Regards,
Wayne DelRossi
Alon N5618F
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Fuel Tank Dipstick Calibration.xls
Description: Binary data
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