Chapter 21: Installing Fuel Lines, Vent Lines, and Sumps

Sump Holes

While at Walmart, I came across some neat sink drain strainers that I could simply flox over the sump holes.  An alternative is to use Norm Muzzy's idea of using small strainers, cutting the handles off, and floxing them in place.


Fuel Drains

Not having a one-eighth NPT tap, I borrowed one from an on-the-field A&P whom I know only as "Sarge".  He likes keeping track of my progress, so he watched as I started to tap the holes in the aluminum squares for the drain valves.  I started tapping the hole all the way through when he stopped me.  Good thing too!  

Education time!  NPT stands for National Pipe Thread and using an NPT tap results in a hole that is tapered, or conical.  The seal is made in the threads, not the shoulder of the drain valve.  The fit gets tighter as the fitting is advanced into the hole.  So Sarge's advice was to thread the hole, but stop every so often and fit-check the drain valve in the hole.  What you want is a hole tapped deep enough to allow two threads showing on the drain valve when screwed in finger tight.

Howard Rogers, an A&P who participates on the Cozy list, concurred with Sarge.  Howard also offered additional advice.  Use a fuel-compatible sealant compound on the drain valve threads, but keep the sealant away from the last two threads at the fuel end of the fitting.  The seal on pipe threads takes place away from the tip, so there is no need for thread dope in that region.  Excess there can do unwanted things, like extrude out and even partially block the opening or clog the drain holes in the valve itself.  And always exercise extreme caution when removing and replacing the petcocks, as it is fairly easy to screw up the threads (no pun intended) in the aluminum squares.  It is a real pain to replace them!

Who knew there was so much to know about tapping holes????? to hold the aluminum square in place for flox cure?  I simply jammed it in place with a short length of PVC pipe.









Vent Lines

  1. The first thing I'll tell you is to order LOTS more vent line tubing.  The quantity in the chapter kit is only enough for routing the vents out the top of the fuselage -- as it was originally on the Long EZ.  You'll need about 10 feet a side to rout up, around the turtleback, and down and out the other side.  You'll need more if you're running the vents out to the end of the strake, even more if you're going to use two vent lines per tank, and still more to account for screw-ups.  Take an extension cord, route it like you would your vent lines, then measure how much tubing you'll need.  Add a few extra feet for screw-ups! :-)  

  2. The second thing I'll tell you is don't even attempt to bend this tubing without the proper tool.  The tubing is very soft and is easily crimped.  Do yourself a favor and buy, rent, borrow, or steal a good radius bender from Mr. Snap-On Tools.  

  3. Take about 6 inches of each type of tubing and become familiar with the distance taken up by 90-degree bends.  You'll need to know this distance when measuring where to place the bends when running the fuel tubing in the fuselage. 

  4. The pictures in the back of the Chapter 21 plans show that the vent lines are basically unsupported inside the tank.  While Nat assures me that the vent line is strong enough to support its own weight, I went ahead and routed it along the bulkheads and taped it down with BID patches.

  1. (Updated 8-24-10) If you are an astute visitor to this web site, then you know I drilled three little holes into the vent lines just before they exit the aft, inboard corners of the strakes.  I did this based on what I now consider to be bad advice.  (Never follow bad advice.)  The idea was to be able to vent the tanks when the plane is parked on its nose without adding a second line.  I installed the vent lines and drilled these now infamous holes in 2001.  It's now 9 years later (2010) and I've decided to cover up those holes.  To fix it, I opened a 6-inch hole into the bottom of the strakes and will cover the three little holes with a ply of BID.  It's not necessary to replace the vent line. I just need to cover the three holes.  I removed the micro and got down to bare glass.  I routed a groove through the external skin and removed the foam with a screw driver.  I sliced through the inner skin using a soldering iron with a flat bladed tip.  This worked great!  It cuts the skin without without sawing and without creating debris. (This is the same technique I'm going to use to install the gas caps.)  I covered the three holes with a ply of BID.  However, the BID ply wouldn't wrap around or stay attached to the vent line tubing.  So I had to apply a pad of flox over the BID ply to help it stay in place.  Next, I made a 1-BID sheet, allowed it to cure, then cut out two "doughnuts" that were floxed onto the inner skin.  These doughnuts allow a one inch overlap onto the inside skin and allow a one inch overlap for the discs that were cut out earlier.  I clamped some foam under the doughnuts to help hold them against the inner skin until the flox cured.  I buttered up the discs with flox and set them onto the doughnuts.  I partially filled the groove with wet flox to ensure the inner skin doesn't leak.  Next steps are to fill what's left of the grooves with micro, then apply 2-BID overlapping the external skins and the discs.  Then I'll fill the area with dry micro, contour to shape, and re-prime.  You'll never know I did this once it's done.



  1. I did run each vent line around the aft side of the firewall, up, over, and around the firewall, and down to an exit point below the opposite strake.  I am contemplating running the vent lines to an exit point at the end of the strakes to keep any fuel spray from the prop arc.

  2. I left the vent lines a little long on purpose.  To assist with future leak testing, I sealed the ends of all lines with very wet flox.  Once leak testing is completed, I'll cut off the floxed ends  This way I won't have to chase leaks at connections!

Fuel Lines and Fuel Valve

  1. The chapter kit contained enough fuel tubing to do the job.

  2. Use a small section of the tubing as a practice piece for determining the distance required for making 45-degree and 90-degree bends.  You need to know this when measuring the total distances for running the tubing in the fuselage.  Get it right the first time because the tubing doesn't take too kindly to being unbent and rebended.

  3. Like everything else, it took a while to figure out how to bend and install the first line; quarter of the time to install the second line.

  4. I ran the fuel lines into the front seat area.  I plan to install the fuel valve in the center console just aft of the throttle quadrant.

  5. I decided to spend the big bucks and get the Andair Left/Right/Both fuel valve.  It's cool-looking plus this three-position valve will give me the best of both worlds.  I can draw fuel from both tanks or I can isolate and run off one tank at a time.  I like the option of drawing off both tanks.  Head pressure will keep the fuel levels equal in both tanks, and if I can see one fuel site gage, I'm confident the other will be about the same.

  6. I decided to cover the fuel lines behind the front seatback with strips of foam.  I didn't want the fuel lines dented or squashed by luggage that might fall onto them.  So I made these from some thick foam.  I installed them over the fuel lines with 1-BID.


Fuel Probes

I thought about installing fuel probes in the tanks, but I didn't want to go through the hassles of figuring out how to install them.  The senders I was accustomed to seeing have the sensor head attached to the capacitance tube.  The sensor head looks like a hockey puck.  It is about 1 inch thick and three inches or so in diameter.   If you want to cosmetically hide the sensor head, then you must bury it under the surface of the strake skin.  This requires building a hidden pocket under the top strake skin like Brian Deford did.  You can also install this type of sensor by drilling a huge hole into one of the bulkheads inside the baggage area.  But sealing the sensor head is challenging and the system is prone to leaks.


Neither of these ideas sounded attractive to me.  The strakes are hard enough to build already, so I decided just to blow off the fuel probes altogether.  After all, I do have sight glasses.  I'll have a fuel flow totalizer.  And I do have a STOPWATCH!


Well guess what?  After flying with Marc Z to Sun-N-Fun 2003, I found it very inconvenient to actually check the fuel site glasses in flight.  I'm not Linda Blair and I couldn't twist my head far enough to see both site glasses.  Using a mirror to view the site glasses is a royal pain in the patooty.  And you can't see the site glasses at all when the aft compartment is packed with luggage.  Marc Z put fuel probes in his strakes and it was comforting being able to see the fuel quantity on the gage on the instrument panel.  At that same Sun-N-Fun, I found these nice Princeton capacitive fuel probes with remotely-mounted sensor heads! 




I changed my mind and I retrofitted fuel probes into the strakes.  What I did was to drill and tap 1/8th NPT holes into 1-inch square pieces of quarter inch aluminum plate.   The probes come with a 1/8th NPT male fitting that will screw into these aluminum squares.  I very carefully chose a spot in the aft inboard corner of each strake where the probe could be inserted straight down into the tank without hitting the fuselage sidewall, front face of the spar, the mesh screens covering the sump hole, the vent line, and most importantly be completely under the cosmetic strake fairing.  I very carefully marked the outline of the squares onto the top strake skin and very carefully cut away the top skin.  I then hollowed out the foam, revealing the inside skin.  I did this first so that debris would not enter the tank.  The measured the diameter of the probe's capacitance tube and drilled a slightly larger hole into the strakes at the chosen location.  You can see the 1-inch aluminum square and the hollowed out area in the pictures below. 


Next, I carefully measured the depth of the tank and even more carefully cut the probe to length so that the probe was the recommended 1/8th inch off the bottom of the tank.  I floxed the aluminum squares in place, screwed in the probes, and applied more wet flox in and around to edges to ensure a good seal. 


I originally thought I'd install the remote electronics boxes inside the turtleback, but I was unwilling to drill a fair-sized hole through the reinforcing layups for the engine mount.  (The probes cannot be disconnected from the electronics boxes.)  I changed my mind and decided to mount the boxes on the firewall.  So I drilled a fair-sized hole in the cosmetic firewall pieces so I could install the fuel probes into the strakes. 


After finishing the cosmetic strake fairings in Chapter 24, the probes and wires were completely hidden!  I decided against making a small access door, but I did measure the exact location and noted it into the plans in case I have to troubleshoot the probes later.  I am a happy camper now!  You want some of these probes?  Call Todd Stehouwer, 616-281-5193, or email him at





Sump Blisters

  1. I carved blocks of blue foam and simply duct-taped them in place on the fuselage/strake bottoms.  Used a nice, wet layup and peel-plied the outer surfaces of the sump blisters.

  2. After removing and trimming up the sump blisters, I prep sanded everything, opened up the sump holes, then floxed the sump blisters in place.  For good measure, I applied a small bead of very wet flox on the seam before glassing with 1-BID tapes and peel-plying.