Air bubble of doom in gascolator!

[4BravoWhiskey]

Actually, now that I think about it more, I just needed a richer mixture to keep the engine running, and more throttle to get our butts to the nearest airport as soon as possible!!

[c170b53]

I would temp remove the FF xdcr, install a new line for TS purposes. The Xdcr is the component that's has altered your system and the last maintenance done since the problem arose. It could be the new part, the installation of the part, is it the right Xdcr for your install or something out there as in A displaced piece of rubber on the inside of a newly fabricated hose (nipple being screwed in and gouging the internal wall) could be acting like a check valve or some other weird thing but I would rule the recent maintenance out as my first step.

[blueldr]

I think you might have a good idea tbnere, Jim, I've seen a rubber flap on the inside of an improperly installed hose fitting. That kind of a flap is capable of becoming a "check valve" depending on the direction of flow.

[4BravoWhiskey]

I'll try that. My mechanic made new fuel hoses for this installation rather than cutting the old one to insert the sensor. He said that cutting/re-using the old ones can result in such problems so he never does that. And I had no fuel issues for 80 flight hours or so. But yes, taking that out of the equation makes sense.

I did also have the rubber hose connections in the vent lines changed in Oregon on my way north to Alaska earlier in the summer. One was leaking fuel during flight. The old ones were quite brittle. I suppose it's possible some rubber bits could have gotten into the fuel tanks that way, and made their way further along. Still don't see how that would result in air, but...

It seems the only thing to do at this point is isolate as many parts of the system as possible one by one, and try it out each time. Unfortunately it is not consistent so that could take a while, and could result in more in-flight excitement. Maybe I could even cap off the primer connection at the gascolator (although I can't seem to start this engine without some primer... pumping the throttle doesn't do it, even if it's warm. Could that indicate a problem with the accelerator pump?).

[blueldr]

If a proper sized mandrel is not used in the fabrication of a rubber hose, there is a very good possibility of the sharp end of the connector cutting into the rubber aa it is screwed in and making an obstructing flap,

[flyboy122]

Thanks for the input guys.

daedaluscan and flyboy122 - I checked fuel flow from both tanks (separately and together) at the input to the carb, and it seemed plenty good, flowed fast a although I didn't actually measure it (gallons/min). I should do that. It flows fast and fine when I just open the valve at the bottom of the gascolator.

.

Let it flow for a while, 3-4 gallons. On my plane it would take a couple gallons to show up. (The PA12 has a sump. The 170 is different, I know, but worth a try anyway.) I would disconnect the line at the carb. If you experience a slow down, then you can work you way back in the system until you isolate the problem.


DEM

[bagarre]

If a proper sized mandrel is not used in the fabrication of a rubber hose, there is a very good possibility of the sharp end of the connector cutting into the rubber aa it is screwed in and making an obstructing flap,

^^that. Always use a mandrel to make hoses.

The flap of rubber can cause a nightmare to trobleshooting.
Try blowing compressed air at a high volume in both directions.

[n3833v]

You can most always see the flap of cut rubber by inspecting. Just maybe the "air" bubble is a vacuum bubble from a restriction. I hope you can find this problem before something happens.

John

[minton]

Inlet and outlet have been mentioned but I have seen no response.

[MoonlightVFR]

Your selected title for initial post is quite descriptive. "Bubble of Doom"

May I respectfully suggest that you do not become airborne in this aircraft until you sleuth this problem with an effective solution.

This forum is the right place for your topic. You perhaps have solved this already as I write this response.

Go back to G A HORN'S comment. Gascolator Gasket. It is so simple in concept, 100's of 1,000's function on all types vehicles without
problem. Not so.

Your fuel system is SUCKING AIR. In medical terms you might think induced air embolism. It could be a NEW Gascolator gasket just installed that did not seal properly or it could be
a new fabricated fuel line with an interior ply that is partially separated, just barely . It's next movement may be full separation : fuel stoppage 100%. Suddenly it is very quiet.

There was an AD on aviation Gascolator gasket. Not a Cessna. I don't remember the aircraft. Design of the mounting bracket , vibration over years, age of gasket were all written up.



I was concerned about aging gasket on my C 170B Gascolator and had my AP/IA install a new one. I was at the shop as it was installed. New Gasket. When he moved the lever to drain a sample. Nothing came out. We looked at each other with a blank expression. Fuel flow interrupted, new gasket was professionally tight.

Reinstalled same new gasket. 20 plus years, no problems.

[dlinsley]

I believe that the problem is from excessive length of the line from the gascolator to the carburetor. It will droop too much, there is not enough flow during normal operation to push the air through but with the line disconnected at the carb there is enough flow to push the air through the low spot and out.

[blueldr]

There was an above comment to the effect that it was "sucking air" fom someplace. I cannot immagine where there could be a negative pressure in the fuel line or where a negative pressure could develop. The negtive pressure developed by the fuel level in the carburetor bowl would be entirely too small to measure without a scientific i strument.

[bagarre]

I was concerned about aging gasket on my C 170B Gascolator and had my AP/IA install a new one. I was at the shop as it was installed. New Gasket. When he moved the lever to drain a sample. Nothing came out. We looked at each other with a blank expression. Fuel flow interrupted, new gasket was professionally tight.

Reinstalled same new gasket. 20 plus years, no problems.

That happens to me when I try to drain the gascolator with the fuel valve shut off.

[4BravoWhiskey]

Thanks again for the additional input, guys. Work got in the way of fun stuff, and I haven't been able to get back to the airplane... hopefully Friday. I want to be there instead of just having the mechanic do it.

I forgot to order new gascolator gaskets, will do that. Sure can't hurt. But I agree with blueldr about suction. The hydraulic head from the fuel in the system will be far greater than any vacuum produced at the carburetor, so while there is suction, is it insignificant compared to that positive pressure.

And good advice to not fly it until I get this sorted out. I'm hoping it's the relatively new fuel line. As for its length, there is no extra length to the hose either between gascolator and fuel flow sensor, or from there to the carb. Just enough to give it a bit of flex and no tension.

[dunlaps3]

Wow , you got me curious about this one. Let's see , hummmm , a tried and true fuel system that has worked for decades . Not experimental. The only thing that I have seen is many years ago I used to have an Ercoupe , same type fuel system. Head of fuel from the tank down to a glass bowl gasculator and then to the carb. Simple , no leaks. I open my cowl one summer day and see my clear fuel bowl half full of air. What the ...?? I don't like that ! I loosen a line and purge the air out. Then on another day , I see the same thing. I do the same thing. Then again on another day. I was using mostly MOGAS in my Coupe . I saw that the more the blend of " Stupid Car Gas " and less Avgas - the more Air in bowl. From that time on it was never more than 50/50 Mogas/Avgas for me. At that level I never got Air in the bowl. I never had running problems , but in my mind , Vapor lock was going to happen. I do not like to fly any plane with more than 50% Car gas. Now if you tell me that you don't use Car Gas , then I am at a loss , but still curious about your problem. Andrew