Fuel system advice

[TJay 1041]

Hey guys I need some fuel system advice here, I am debating weather to run gravity feed with a back up electric pump on my kitfox and eliminate the mechanical fuel pump, I have plenty of fuel flow at the fire wall,  but the fuel line needs to make a funny angle and raise up 2 inches to hit the carb, I know Jim has had success running gravity, But this funny bend has me worried, Have a look at my picture, I made a mock up sample fuel line and taped it to the fire wall to show you guys what it will do, Lets hear some thoughts

[chopndrag 226]

Never hurts to have a mechanical pump running full time and use the electric as backup 

[1avidflyer 1983]

Problem with the mechanical pump on the Jabiru, is sometimes it can overpower the float needle valve and flood the engine.  I had an engine out that way once.  I'm looking at my old pictures TJay, and I think my fuel line came out where yours did.  I just turned it down and hooked it to the carb when I got rid of my fuel pump.  My fuel valve was right next to the throttle, and went pretty much straight forward and through the firewall.  JImChuk

[EDMO 1078]

Your bend should not affect the gravity pressure since you are almost the same distance below the tanks - I might think about putting some sort of part/guard between the exhaust and fuel line to block the heat and prevent possible vapor lock.   EDMO

Edited 21 Feb 2017 by EDMO

[Ironman Al 35]

I used an adjustable fuel pressure unit on my kitfox after the mechanical pump and adjusted it to the electric pump with the engine off! 5.5 lbs. Will gravity flow fuel past your electric pump when its off? Or will you run it in tandem to the main line?

[tx_swordguy 20]

after having an engine out (rotax 582) thinking my electric pump should only be used as a back up as needed (take off/ landing), I am of the opinion two or more pumps on all the time. If you have too much pressure than get a pressure regulator. My engine out= about 5 gallons in wing tank electric pump off, mechanical pump on(with gravity). It started sputtering and running so badly as to get the "oh shit pucker" going. I looked over and fuel pressure was almost non existent. I turned on electric pump and it roared back to life within seconds and ran without a hiccup back to the airport. (2nd or 3rd flight of a new to me airplane). Lesson learned was always have the electric pump on because even with the mechanical pumping it would not draw enough through to run the engine. It ran on mech/gravity only for about 45 min until I burned enough fuel that the weight of the fuel was not enough to push it through the electric pump (at least that is my take on it) 1/4" fuel line takes more pressure than you might realize to move fuel up to the carbs especially if you are using alot  throttle. It never totally gave out but it was DEFINITELY not making power and I was not holding altitude. One thing you might not realize is all the attitude changes you have while flying can play into how much fuel your carbs get (another story). In a car the entire fuel system is level. If you bank one way for a while you may lose fuel to your header for a little while and it may take longer than you want for gravity to catch up. My opinion is a mechanical is cheap insurance. If you do lose the mechanical, run the electric ALL the time not as here and there when you think you need it.

Edited 21 Feb 2017 by tx_swordguy

[EDMO 1078]

Question:  If you run the electrical back-up pump all the time, then how do you know if the mechanical pump is working or has quit, and the electrical pump has become your only primary pump?  EDMO

after having an engine out (rotax 582) thinking my electric pump should only be used as a back up as needed (take off/ landing), I am of the opinion two or more pumps on all the time. If you have too much pressure than get a pressure regulator. My engine out= about 5 gallons in wing tank electric pump off, mechanical pump on(with gravity). It started sputtering and running so badly as to get the "oh shit pucker" going. I looked over and fuel pressure was almost non existent. I turned on electric pump and it roared back to life within seconds and ran without a hiccup back to the airport. (2nd or 3rd flight of a new to me airplane). Lesson learned was always have the electric pump on because even with the mechanical pumping it would not draw enough through to run the engine. It ran on mech/gravity only for about 45 min until I burned enough fuel that the weight of the fuel was not enough to push it through the electric pump (at least that is my take on it) 1/4" fuel line takes more pressure than you might realize to move fuel up to the carbs especially if you are using alot  throttle. It never totally gave out but it was DEFINITELY not making power and I was not holding altitude. One thing you might not realize is all the attitude changes you have while flying can play into how much fuel your carbs get (another story). In a car the entire fuel system is level. If you bank one way for a while you may lose fuel to your header for a little while and it may take longer than you want for gravity to catch up. My opinion is a mechanical is cheap insurance. If you do lose the mechanical, run the electric ALL the time not as here and there when you think you need it.

[1avidflyer 1983]

If it isn't there, it can't quit.  If you run mechanical, and electric pump plus the fuel pressure regulator, you have that many more things that can fail.  Champs, Chiefs, Cubs and who knows what other planes flew just fine on good old gravity.  Obviously different planes require different equiptment, but if you can do without it you are probably better off.  Everybody has to do what they are comfortable with.  And some of us will get into trouble for doing just that.  ;-)  JImChuk 

PS  tx_swordguy,  what kind of airplane were you flying that had the problems you describe?  If an Avid or Kitfox, you really should have the ram air tubes on the wing tank covers, and they NEED TO POINT FORWARD. 

Edited 21 Feb 2017 by 1avidflyer

[kosseman 3]

a gravity flow carb most times has a larger needle and seat to let in more fuel at the lower pressure something to think about

[1avidflyer 1983]

a gravity flow carb most times has a larger needle and seat to let in more fuel at the lower pressure something to think about

Jabiru supplied a 1.5 MM float jet for their bing carbs.  If you run gravity feed, Bing recommends using their 3 MM jet.  I flew with gravity feed in my Avid MK IV for many hours with the standard jet.  I did use an electric pump for takeoffs, although the one time I forgot to turn it on, I didn't notice it running out of fuel but turned it on after I was 20 or 30' in the air.  JImChuk

[TJay 1041]

Well I called Pete at Jabiru today and he said before you start cutting your counsel apart to re wrought fuel lines try a different spring in the pump, He is sending me one he says that pump should put out 2psi Max and mine is at 4.5psi He claims the weaker spring will lower the pressure, He also says every Jabiru high wing he has ever flown in has the engine driven pump. Its kind of like Jim says Everybody has to do what there comfortable with, Guess for some reason I need positive fuel pressure ha, I see an awful lot of Rotax engines out there running a fuel pump, Think I can make her work,

[tx_swordguy 20]

1avidflyer= I was flying an avid flyer c model with a rotax 582. I did not build it I am the third owner and airframe has over 1200hrs. There may be a kink in the fuel line somewhere that I am not seeing so I cannot count that out. What I do know is that I have not had any trouble with fuel flow if both the electric pump and the mechanical pump are working. We all must do what we feel comfy with. Me I feel comfortable with electric AND mechanical fuel pumps installed and operating.

 

[1avidflyer 1983]

The 582 Rotax uses 2 type 54 Bing carbs.    The Jabiru uses 1 type 94 bing carb.  Probably we are comparing apples to oranges on what they will tolerate for fuel pressure.  JImChuk