Friday, August 15, 2014

progress in the fuel system!

As you will recall, I left off with the conclusion that the fuel pump was the next suspect, and I was awaiting its replacement.   I had been thinking about how to test the pump and went to the local auto parts store to get some tubing and adaptors so I could pump gas from the gas can back into itself.  I hooked up the old pump and got the familiar low hum and no gas flow.  I hooked up the new pump and got a moderately louder hum but... ... no flow.  Now I was really intrigued (I’d long passed the stage of anger/frustration—now it was a puzzle to be figured out.)  The odds of two bad pumps were so low that it wasn’t worth thinking about any further.  Next step?  The power supply. 

I was using an old battery charger that I’ve owned for a long time.  (You can tell where this is going, eh?)  Pulled out a volt meter and measured 11.5 vdc.  That’s odd, it should be about 14 vdc to charge a 12 v battery.  I put one of the pumps on the charger and still got 11.5 vdc.  Just on a whim I checked for AC and found 35 vAC!  That’s definitely Not Good.

An emergency run to the 24 Hour Aviation Supply Store (a.k.a. WalMart) resulted in their last two 6v lantern batteries (one alkaline, one ‘standard’) and this time I could pump gas through the test circuit!  With both fuel pumps!  From here, it was all down hill (in a good way).  Installed the old pump into the plane, added 2 gal of gas and the ‘short’ between the gascolator and the return line.  It pumped fine and there was good flow out of the return line back into the tank.  I let it run about 10 min with no gross leaks.

IMG 3536

Gas dribbling down return line

(The photo doesn’t show it very well, but there is gasoline dribbling down from the inside of the yellow fill funnel and along the fuel return line.  (I used the yellow fill funnel to keep gas from splashing all over everything.)  Even though it’s a lousy picture, I was still quite pleased with the occasion, so here it is.)

Removed the ‘short’ and let the system pump gas back into the can.  When the tank was dry, I used one of the suggestions from VAF and wedged a steel rod threaded through a funnel to drain the gascolator into the can.  viola!

Now that I finally have figured out that problem, I was raring to get going on the wiring.  I got 6 or 7 pages done in 24 hours, but will have to take another 1 week break and go back to work. 

Alas, not all is completely wonderful.  About 4 hours later I was pulling wires through the belly access plates and noted a wet connector where the forward fuel return line attaches to the bulkhead union.  I’m pretty sure that I cross threaded that connection when I had so much trouble installing it.  I re-installed the connector with a new thread sealant (the one recommended by Bob) and will re-test the fuel system when I’m able to spend a day flipping the plane back onto its belly.  I expect that it’s going to leak and I’ll need to replace that line and the bulkhead union.  Stay tuned!

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