First, Build a Shed

[Cherrybark]

It appears, looking at this photo of a fuel flow test on a Zenith in 2013, that I'll need to organize:

• At least one steel beam across the top of the hanger
• A steel cable with block and tackle
• A crew with possibly two strong men, a young boy, and a mule
• And a few other odds and ends that I haven't figured out yet

[Av8r_Sed]

Here’s a straightforward procedure you can follow: http://mybearhawk.com/finish/fuelflow.html

[jiott]

Exactly the same as mine.

[efwd]

If it is an ignition problem then I have lost all confidence in the redundancy of the computers on the 912iS. His lane lights are checking out OK. I honestly can't say I know what happens if you don't have a fuel return line that is functioning but the fuel injection requires it if I recollect. I understand that the UL versions run without a return but the return line was added in order to prevent vapor lock on those engines. Certainly someone like Larry will know more.

[Eric Page]

Plug wire not seated on a spark plug? Like I said, I have no experience with Rotaxes.

[Cherrybark]

Had a text exchange with Eddie this afternoon and he cleared up the purpose of the plumbing loop on the Fine Filter Sub-Assembly. He did suggest I double check so I'll post my understanding. The "Out" line from the dual fuel pump box runs to the fitting marked XB on an aluminum block. That block has three other outlets, the most obvious being a location for my fuel pressure sensor. A second fitting supplies fuel to the large, "Gemini capsule" shaped can on the upper part of the U-shaped loop. This is a fine fuel filter and needs to be correctly oriented. The third fitting supplies a "pop-off" valve set at 17 PSI. This is also a directional element. For the life of me, I couldn't understand the point of this loop or what the 17 PSI valve was all about until Eddie explained. Should the fine fuel filter become clogged, fuel pressure will eventually build to 17 PSI and the pop-off valve will open and continue supplying fuel to the engine. In summary, there are two possible sources of fuel to the T fitting XG which is were the fuel line to the engine rail is connected.

Just to double check my work, and remembering that engine and airplane references are based on the view from the pilot's seat, I ran a fuel line from the XG T-fitting to the rail on the right side of the engine. Is this correct?

Made a quick visit to the hanger today but no time to work on the plane.

• The 17-PSI pop-off valve is installed backwards. At least, my hand drawn flow arrow, points towards the aluminum block. I thought reversing this would fix any fuel flow problem then realized it's very unlikely the brand new, fine fuel filter is clogged. Obviously the valve needs reversing. And I'll examine it closely to double check that my arrow points in the right direction.
• The header tank return line check valve, located under the center console, is oriented correctly. This unit has a clearly marked flow direction as, in my opinion, all of these units naturally should.

This weekend I'll have a mechanical fuel pressure gauge available for testing. I'll measure the pressure at the pump outlet and at the engine. it would be great if a simple plumbing restriction was the issue. If the engine is not running, does fuel flow freely to the header tank return line? Or does PSI just build to the pump limit at the engine input since the injection isn't running?

If there is 40 or so PSI at the input to the engine, I'll be jiggling ignition wires, calling Kitfox, and wondering what to look for next.

Oh, first one to fly into East Texas and point to the problem, get's a free Combo Plate at the Purple Pig BBQ joint just down the road!