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fuel pressure problems


samifer

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So i made the mistake of draining all my lastyears fuel untill it did not run out of the drain.

This introduced a bunch of air into the fuel system and i cant seem to purg it out and i cant find a fuel purge instructions in the manual. A bunch of air comes out of the drain every time i run the plane on the ground for a few mins

Can anyone help me out?

I have a 2010 ctls

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Hi Samifer,

 

Don't worry about the air in the fuel system. Just get the engine started and let it run for a while. The air won't hurt anything. There is no fuel/ air purge procedure.

 

but since you brought it up you could purge from the tank all the way to a carb if you wanted to. Pull either the fuel line off the out side of the fuel pump or off one carb. Take the fuel tank cap off. Fill the wing tank up to 10 gals. or more.  Take a low pressure air hose and place it up to the edge of the tank and plug the rest with a rag. You only need a few psi to move fuel through the system. Some will go over to the other tank unless you clamp that fuel line off down in the cockpit.

The fuel system is completely open and free flowing so just a little pressure with an open end will move the fuel through.

 

Before anyone goes up in arms over pressuring the fuel tank that is not what you are trying to accomplish. You only need a few psi over ambient to move the fuel which will not hurt the tank and it isn't closed to real pressure build up because you are using a rag to help seal which is not air tight and fuel/pressure can move freely to the other open vented tank and down and out the open fuel hose.

 

But you really don't need to do this. 

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All day now i have been purging air out of the drain and it does not seem to stop

i filled the plane up with marked premium this morn and have never used it 100% before. ...... could this fuel be turning into a gass?? I just drained out 40 liters and replaced with 100LL and it is now holding 3.5 psi at 75% throttle but still has air bubbles when draining and presure drops to 2 psi randomly

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The air is in your system in high spots. It will come out over time. Just because you have some air in the system doesn't mean the engine will quit. As the air gets to a pressure sender or a fuel flow transducer these do not read air so the readings for a while will move around until all air is eventually gone. It has nothing to do between 100LL and Auto fuel. Yo are going to have air for a while. Just run the engine and it will fly just fine. The fuel didn't fix the problem. It was when you did a drain that some air came out.

 

Sounds like the engine is running so let it run a while.  What if like many you didn't have a fuel pressure gauge or fuel flow. You would never know the difference and just go fly. Too many gauges and readings can play with your head.

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Hi Sam!

 

We use float carbs, and they don't care about air (air just gets vented to the intake manifold). We have no centrifugal pumps, so you don't need to worry about fluid priming. Since we use high wings, head pressure prevents vapor lock from being an issue.

 

You won't be able to stop air from being in your lines, because the moment you shut down, the heat from the engine will warm the lines and a little will vaporize.

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Right, no fuel means no boom, but air in the lines will purge out of the carb vent lines just fine.

 

There is one thing about flight design's setup that I don't like. Rotax recommends the return line go to a fuel or header tank, even in the carbureted engine. If they did so, it would purge the air automatically, but instead it's recirculated to the gascolator. It's not a bad setup, but it's not the preferred setup.

 

The worst type of setup are those that have no circulating system, and rotax strongly discourages them.

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FYI if Float carbs get no fuel, engine still dies

 

If no fuel in the carb bowls you have a blockage or a pump issue.  air will not disrupt fuel flow.  the fuel pumps also dont care about a little air in the line. 

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