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Fuel flow issue.


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Posted

My brother recently bought a KF Classic IV. While doing taxi tests, it ran for about an hour and a half, then quit. The EIS said Low Fuel Pressure. He loaded it on the trailer and took it home, where it promptly started and ran on the trailer with the wings folded back. He was unable to find any problems. About two weeks later, he was flying with an Instructor, and after about an hour and a hale, it quit in the air. Again "Low fuel Pressure". They tried a successful re- start. They made it down safely, and he loaded it and trailered it to my place for diagnosis. We talked to Lockwood, and Kitfox, and the best suggestion we could come up with was possible vapor lock. Unlikely in the air since it was cool that day. We began checking the fuel system end for end. Eventually we found the problem. The fuel line where it exited the wing and entered the fuselage had been fastened to the carry through inside the fuselage. This caused the lines to kink in the wing root when the wings were folded forward. When the tanks were full there was enough head pressure to keep the header tank full. When the head pressure went down, the kink prevented adequate fuel flow. What threw us a curve was there is a low level sensor in the header tank that never came on. Turns out it was defective. The "test" button on the instrument panel only tests the indicator light, not the unit.

We replaced the hoses with AEROQUIP steel braided hose, and put a new sensor in the header tank . Added two items to the preflight and run up to: 1. run the electric fuel pump without starting the engine and check the pressure to confirm it works, and 2. Run the engine with the wing tanks shut off to confirm the low level sensor in the header tank is working.

 

Bob McCaa

 

 

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Posted (edited)

Another test you might run ON THE GROUND, would be to shut off the electric pump and see if engine will continue running.   Some have free flow when off and others block the flow.    EDMO

Edited by EDMO

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Posted

Thanks for this thread. Oftentimes guys post about a problem and we never get to see what the fix was. We can all learn from this type of stuff. Fuel starvation is the #1 cause of stoppage in small airplanes and all too often people blame the 2-stroke. I once heard someone say that most two-strokes don't die they are murdered and I fully agree. 

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Posted

Thanks for the input. Have already done the fuel pump tests. The pumps are in series, with a by-pass check valve in parallel with the electric pump, which is a Facett. Fuel pressure with the Facett alone is about .3 Bar, and with the mechanical alone is about .4 Bar. (PSI= 14.7 x Bar) We did a free flow test after the work was done and with five gallons in each tank, it flowed about a half gallon per minute from either tank  through the header tank without the pumps running. The engine is a Rotax 912 80 HP and burns about five gallons per hour in climb, so we are more than adequate using either or both.

My Avids are 582 gray heads, and I agree with C5engineer.

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Posted (edited)

I had a similar occurrence when I watched my upstream fuel filter empty itself as I flew, indicating I was burning gas faster than the tank was delivering it. I landed at the nearest airport and saw that the bronze screen in the fuel tank pickup had clogged with small stuff. I removed that screen and things got better fast. The original builder, Jim Peet, made sure that a clear filter was put near the input to the header tank, in easy sight of the pilot, so that a glance every now and then can assure that a steady stream of fuel is refilling the header tank. I show a shot of 52X with the yellow filter just visible inside the left door. Maybe everybody has this filter.

P1010188.jpg

Edited by nlappos

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Posted

Avid very strongly advised against having a filter between the wing tanks and the header tank.  Not a lot of head pressure in the tanks, and it doesn't take much to clog the filter and shut down flow.  Also the header tank acts as a large gascolator. so a filter past the header tank is far less likely to get junk in it to clog.  I had one off field landing before I got rid of the filters just down stream of the fuel tanks.  JImChuk

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Posted

Jim,

I found this in my older files, it recommends that filter. Is there a later warning?

Nick

filter.jpg

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Posted

I'm not aware of a letter advising against the fuel filter.  When I had my off field landing back in about 2008, I asked questions about it on this site.  Steve Winder was fairly active on here then, and his reply said not to have the filter before the header tank, for the reasons I mentioned.  I tried to find those posts in a search, but only found stuff back to 2009.  I'll post it if I find it.  I wasn't aware of your letter either for that matter.  JImChuk

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Posted

i have two of these and they are mounted above the back of the seat were you can see the fuel moving. You need to put a cotter pin to keep the thumb screw holding the filter in case it comes loose. I have read that if it does come loose with out a pin, it may unscrew so far as to obstruct the fuel flow.

720-9748.jpg

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Posted

Those glass filters is what I have always used as they can be visually checked,I mount them on standoffs to minimise vibration and have never had a leak or any problems.

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Posted

i have two of these and they are mounted above the back of the seat were you can see the fuel moving. You need to put a cotter pin to keep the thumb screw holding the filter in case it comes loose. I have read that if it does come loose with out a pin, it may unscrew so far as to obstruct the fuel flow.

720-9748.jpg

Same filters I use.  They work great and can be cleaned very quickly! 

I have the plastic kitfox header tank in mine.  If fuel is not flowing into it I can run about 15 minutes.  Just enough time to warm up, taxi and get to a really shitty altitude.  Yes, I have found that out the hard way!  I am anal about checking the filters and watching the hoses coming out of the wings.  I can see the fuel flow pretty clearly in them.  I also watch the fuel flow meter closely on take off and low level flying now.

Glad he didn't bend his bird before he got it sorted out!

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Posted

The prime cause of General Aviation accidents is the pilot putting too much air in the fuel tanks.

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Posted

I don't do that... but flow restriction from main to header tank has gotten me.

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Posted

I have two objections to those filters (1) very small filter area and (2) if plugged with fiberglass or nearly so you can't see it, ask me how I found out that with my Q2 many years ago.  :bugeyes:

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Posted

I have two objections to those filters (1) very small filter area and (2) if plugged with fiberglass or nearly so you can't see it, ask me how I found out that with my Q2 many years ago.  :bugeyes:

And paper filters shouldn't be used - So what do you suggest Paul?  EDMO

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Posted

I have one filter coming from my tank then 1 on each line going to the carbs for added protection . 

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Posted

Very valid point, WY Paul.  Fiberglass can be transparent and thus hard to see.  Fuel strainers should be in the tanks, so that keeps the big stuff out of the lines, then the header tank/ gascolator gets a shot at the stuff that gets through.  If anything gets past the tank, then a filter will stop it getting to the carbs.   That's how mine is and I'm sticking with it.  JImChuk

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Posted

Like Chopndrag I have the little filters in my two carb lines (sinistered bronze) but my main filter in both of my planes are the pleated paper.  I've heard the arguments against them but I have over two million miles behind paper filters that have worked without problems.  The key is to just change them at each oil change.  I would be interested in seeing some data that might make me question my experience although.

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Posted

Had this glass type fuel filter here in canada and Transport Canada inspector made me remove it because they do not accept the glass part....apparently they could crack and leak..also in an accident they would shatter. Last but not least, the plastic mesh inside can get hard and brittle with old age/use and plugs your carbs.

 

My one cent

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Posted (edited)

Had this glass type fuel filter here in canada and Transport Canada inspector made me remove it because they do not accept the glass part....apparently they could crack and leak..also in an accident they would shatter. Last but not least, the plastic mesh inside can get hard and brittle with old age/use and plugs your carbs.

 

My one cent

I read long ago that Canada required metal fuel lines inside the cockpit - hearing now that they don't require that - what is the understanding that you know of?   I probably wont fly thru Canada again anyway.   EDMO

Edited by EDMO

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Posted

I personally do not like filtering gravity flow.  I didn't and won't ever put filters between the wing tanks and header tank.  

Filtering pumped flow is more positive in the case of a partially blocked filter.  I have a large metal case filter just prior to the mechanical pump in the Mangy.  I replace it every 50 hours or annual, whichever is first.  $10 from NAPA.

 

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Posted

These filters won't flow? Surface area not big enough? :blink: I have one on my hot rod boat on the suction side of a 130 GPH pump  with a return style regulator. The 2 stroke race motor uses 25 GPH at WOT. I have been using these for years (20 or so) without issue. It is a relatively coarse filter. I have two more, one per carb under the cowl.

As far as fiberglass, I think I could see it. Plus I flushed my tanks well and found no debris. Plus with two of them, both plugging would be highly unlikely, IMO.

As far as the plastic being brittle, never had that happen. But I would think you would find that during the condition inspection. And my plane is hangered.

And the glass breaking in a crash? For one you aren't supposed to crash. And two the tanks could rupture, fuel lines could be cut, etc, etc. The glass is very thick!

I did a bit of research and none of your concerns were mentioned. Just the cotter pin keeping the thumb screw so where it wouldn't back off if it came loose. That was the only experimental aviation failure I heard about.

BUT each to his own. :)

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Posted

Note the Conclusion of the Avid AD letter I posted, "Avid recommends that a clear filter be installed at the inlet to the header tank."

But to each his own!

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Posted

Huh? My disagreement was not with you for one thing... ? What made you think that? If you read my posts, I have two "see through" filters on the RH side FLOWING INTO THE HEADER above seat. Anytime during flight I can glance over and look at them.

If my race boat can draw 25+ GPH with ONE on the suction side of the fuel pump, this tiny 65 HP Rotax should be fine as wine!!! :lmao:

Maybe you should read the post better before you express your concerns over a discrepancy.

But, each to his own. :rolleyes:

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Posted (edited)

https://www.youtube.com/edit?o=U&video_id=_rHWWiMiA4U

The old boat, 96 mph best. The new boat has over 280 hp and a high pressure pump for the EFI, so the set up to totally different. 110 mph should be NO problem. The problem is conditions and the size of your balls. :bugeyes:

Edited by Fly-n-Low

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