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FlyboyTR
Joined: 04 Nov 2006
Posts: 215
Location: Mobile, Alabama
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 Posted: Sun Oct 25, 2009 4:52 pm Post subject: Fuel Flow Problems, Again! (Vixen, Series-5) |
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We just returned from an 800 mile trip to our favorite flying destination, High Valley Resort in north GA. We developed a fuel flow problem while enroute.
A little history. Two years ago I had a fuel flow problem (actually on the same trip!) that was caused by my “new” paper filters (located between the wing tanks and the header tank) air locking and not allowing fuel to flow. We completed the trip using just one tank. After returning home, I discovered that if I blew up through the fuel line, causing the filter to fill with air, it would not gravity flow! After either sucking on the line ( or blowing on the gas cap vent tube) to force the fuel to flow, it would flow without restriction. This was repeated numerous times, on both tanks with the exact same results! The filters had been replaced just prior to this event. This was also tested with new filters with the same results. After that, I returned to using the filters with the glass sight tubes.
OK…present day... I filled both tanks to the brim prior to our 400 mile, one way, flight. After about 45 minutes Kathy noticed there was no fuel in the header tank vent line. The right tank level was low and the left one was full (could not see the fuel level…above the sight gauge). We checked and both fuel valves were on and we cycled them several times. I reduced power to the engine and set it up lean of peak to reduce the fuel flow. Shortly, fuel appeared in the vent tube (yes that was a relief!). Fortunately we were at 9,500’, talking the Atlanta Center and had an airport with easy gliding distance (which also provided some peace of mind).
After going back to full cruise power, the fuel level in the vent line started dropping. We turned the working tank off, pinched the vent line so it would force, hopefully, the fuel in the right tank to be sucked. After a few seconds, the left tank filter (which was filed with air) starting showing some fuel movement and slowly filled about ½ way. I kept the vent line pinched for about a minute. Fuel flow was established on the left tank, but still not enough to fill the vent line. I turned the right tank back on and the vent line filled. I closed it again and then slowly opened it to allow partial flow and kept the fuel level in the vent line visible for about 30 minutes. After several gallons of fuel was pulled from the left tank, I opened the right valve completely and the vent tube filled. After that fuel flowed from both tanks and was not a problem.
Heading Home… We stopped for fuel while heading home. This time the same thing happened, except the tanks were reversed! Right tank would not flow. We did the same thing…pinching off the vent line and forcing the system to “suck” from the non-flowing tank. Again, this was met with success.
I am at a complete loss! The vent lines on the gas caps are open (checked with each fill-up and also with a pipe cleaner, etc). All my flexible fuel lines are 3/8” marine grade lines (vent line is ¼” clear Tygon). No lines are pinched. Once flowing, they flow with no restriction. There are no loops, etc in any of the lines. I would appreciate any helpful information regarding this problem!
Also…On the return leg home this afternoon…My charging system went out! I just hope it's not “another” alternator coupling/clutch that’s gone bad!
Travis
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_________________
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
www.enotam.net (My Flying Info Website) |
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FlyboyTR
Joined: 04 Nov 2006
Posts: 215
Location: Mobile, Alabama
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| Posted: Mon Oct 26, 2009 10:13 am Post subject: Re: Fuel Flow Problems, Again! (Vixen, Series-5) |
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With permission, I wanted to post an email I received:
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Travis,
My name is Don Smythe. I was on the list for years until I sold my IV. I still read the web version of the list just to keep up but this is the first time I've responded this way.
Fuel flow is one of the problems that seems to hang around and comes back from time to time. I once built a simulated tank/header in my shop and played with fuel flow for hours. I found two things that make a big difference in flow. The first was, a paper filter will clog quickly especially if allowed to see a little water. Second (and most important), if the fuel lines from the tank down to the header are not kept "continuously" down hill they will vapor lock and stop or greatly diminish flow. Any area of those two lines that are allowed to run horizontal is bad (even a short distance)!!!!! Another thing that came up years ago was the clogging of the clear Purolator glass filters. Fiberglass fragments clogged the filters but were invisible to the eye.
I would also do a fuel flow check sitting in the hanger. You must catch the fuel at the same height as the carb. Catching the fuel at the hanger floor will throw off the rate by giving you a higher rate of flow. You should have at least 1 1/5 times the max engine burn rate.
Back in the day I also learned a little bit about vapor lock. It seems that any time fuel passes through a larger body such as a filter it will gas off. I often wondered why my filters appeared to have a little air in them. That's half fuel and half vapor. It seems that's why auto makers started putting their fuel pumps in the fuel tanks vs. at the engine???? I had a good buddy (Michael Harter) that put an aux fuel pump on his Subaru but placed the pump up behind the instrument panel. He had an engine out I believe on his first flight with the pump. Landed OK but later found out that the pump "must" be located at the output of the header. Again, this is probably the old "vapor lock" thing that caused his problem.
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_________________
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
www.enotam.net (My Flying Info Website) |
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FlyboyTR
Joined: 04 Nov 2006
Posts: 215
Location: Mobile, Alabama
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| Posted: Sat Oct 31, 2009 12:12 pm Post subject: Re: Fuel Flow Problems, Again! (Vixen, Series-5) |
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Since this (my original post) was duplicated, I am bumping it so the original post/problem remains close to the thread that is being responded to. 
| | - The Matronics Kitfox-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?Kitfox-List |
|
_________________
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
www.enotam.net (My Flying Info Website) |
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