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Unported my left tank in a slip

All good info and hard to recall. I guess the questions may be: Is the stock PA-18-95 setup described here prone to fuel starvation in a prolonged 20-30 sec left slip with about 1/3 in the left tank? Is his front header positioned correctly or lines (vent/fuel) restricted?

Even in subsequent coordinated descending flight it apparently ran poor until switched to the right tank. If the front header was not full to begin with, or emptied fast, or when isolated from the main tank prone to low flow to the carb somehow, I can understand a lag in response. Make sure the lines don't have an air lock bump. Fix it.

Gary
 
Tangential - I sure do like my headerless system, not having to worry about adding fuel to the header tank before fuel gets to the carb in the event I mess up. I get a re-start in less than 5 seconds from either re-porting an unport, or an incorrect fuel selector setting.
 
One reason for header tanks is in case the fuel tank in use lacks a front outlet. Low on fuel and nose down or uncoordinated flight can unport the rear and cause quiet times. Placards don't fill carbs.

Gary
 
Another way of putting it is with a properly configured header tank like mine apparently is, one advantage is 2 less tank fittings, less fuel line/fittings busy work. Plus I gained 3 gallons capacity, and it's all useable.
 
60F... Humidity?

Possible that it built up carb ice, less direct inlet air suffocated the carb, and once you opened the throttle it came back to life?

Often times we have one thing go wrong, but our moving of other controls make us think it is something else.
 
Screw the weight, I’ll keep my header tanks. AD up front and stock aft, never had an issue and I’ve slipped full left and full right in all fuel loadings.
 
In Post 31 there is a diagram of the fuel system. Up until now, I believed that all header tanks had an inlet were fuel flowed from the main tanks into the header, PLUS an outlet from which fuel flowed out to the engine.

I believe this diagram has enlightened me. It looks like that diagram shows only one fuel line connecting the header to the fuel system, plus a vent line. The fuel line acts as both an inlet and and outlet to supply fuel to the engine. So, under normal operations, the header fills up with fuel and and sits there on standby. If fuel stops flowing from a main wing tank, then the header will start to drain.

Am I reading the diagram right?
 
A both position on the fuel selector valve eliminates this issue.

After unporting the left tank on two occasions-- once almost in the bushes--I installed the STC--Left/ Right/ Both/ Off. Never had a problem since. Another "peace of mind" expenditure.
 
If I still owned a Cub with a similar fuel system I'd duplicate OP MZ18's first post and go see if a prolonged left slip can create an engine stoppage.

Gary
 
With the original super cub fuel system, you should be on the left tank. Which means you slip left wing high...only.
 
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Haven’t had time to troubleshoot any further yet, out of town for work. Regardless of what I find, I’ll probably be replacing my Univair fuel valve with a DakotaCub valve that has a “both” position.
 
Haven’t had time to troubleshoot any further yet, out of town for work. Regardless of what I find, I’ll probably be replacing my Univair fuel valve with a DakotaCub valve that has a “both” position.
I like my Dakota Cub fuel valve with the stock system. I have my head up my ass on occasion and run on the low tank. I run 6-8 gallons of gas a lot and my stupidity was gonna bite me in the but eventually. The right tank feeds slower in cruise but I just work the valve like I did with the original when going cross country.
 
In Post 31 there is a diagram of the fuel system. Up until now, I believed that all header tanks had an inlet were fuel flowed from the main tanks into the header, PLUS an outlet from which fuel flowed out to the engine.

I believe this diagram has enlightened me. It looks like that diagram shows only one fuel line connecting the header to the fuel system, plus a vent line. The fuel line acts as both an inlet and and outlet to supply fuel to the engine. So, under normal operations, the header fills up with fuel and and sits there on standby. If fuel stops flowing from a main wing tank, then the header will start to drain.

Am I reading the diagram right?

Yes, that is how it works. The header vent will act as a forward outlet for the main tank under normal operation,flow will be decreased due to the small diameter of the vent, but it will flow through the header enough to keep the fuel fresh.

On the original question, there is no reason to fly the plane to troubleshoot. Drain the left tank,or jack the right wing if the tank is low, just get the left main tank unported. Disconnect the fuel line at the carb, selector the left tank and a headers worth of fuel should drain out. If the fuel system works correctly, the slip may have caused the carb float to hang up. Just go through the system, make sure it is clean and correctly installed. Lots of old wives tails about headers. Just remember **** runs down hill, it's not that complicated. I do not like the both system for a lot of reasons, but to each their own.
 
I do not like the both system for a lot of reasons, but to each their own.
Would you care to elaborate on this? Differing points of view can be instructive. I like the both position for ease of maintaining balance as well as avoiding issues of unporting as described above. I can always choose to just use left or right, but can never use both if it isn't there. It is important to use either left or right when mooring a seaplane or parking sideways on a hill.
 
I would not trust any diagram/drawing/construction manual as to what the Actual fuel system design is in any of the old cub style aircraft. Through the years who knows what mods have been done to the system documented or not. Take the time to pull some panels and get a good look at exactly how the system works double check the fuel valve that you do get fuel flow when it says you should get fuel flow.
DENNY
 
I would not trust any diagram/drawing/construction manual as to what the Actual fuel system design is in any of the old cub style aircraft. Through the years who knows what mods have been done to the system documented or not. Take the time to pull some panels and get a good look at exactly how the system works double check the fuel valve that you do get fuel flow when it says you should get fuel flow.
DENNY
 
I would not trust any diagram/drawing/construction manual as to what the Actual fuel system design is in any of the old cub style aircraft. Through the years who knows what mods have been done to the system documented or not. Take the time to pull some panels and get a good look at exactly how the system works double check the fuel valve that you do get fuel flow when it says you should get fuel flow.
DENNY

Absolutely. Was at a large maintenance facility years ago with a Falcon 20. One of the items to accomplish on the inspection was to pull the fire handles and verify fuel flow stopped completely to the corresponding engine. Yep, pulled left handle and flow continued to the left engine. It did, however, stop to the right engine. Teleflex cables, hooked up backwards and flown that way for who knows how long.
 
Absolutely. Was at a large maintenance facility years ago with a Falcon 20. One of the items to accomplish on the inspection was to pull the fire handles and verify fuel flow stopped completely to the corresponding engine. Yep, pulled left handle and flow continued to the left engine. It did, however, stop to the right engine. Teleflex cables, hooked up backwards and flown that way for who knows how long.

There have been more than one Cub fuel selector with the handle on 180* out. Also, with the fuel lines connected wrong, it's possible to get the left, right, and 'off' in some unexpected positions.

Web
 
Absolutely. Was at a large maintenance facility years ago with a Falcon 20. One of the items to accomplish on the inspection was to pull the fire handles and verify fuel flow stopped completely to the corresponding engine. Yep, pulled left handle and flow continued to the left engine. It did, however, stop to the right engine. Teleflex cables, hooked up backwards and flown that way for who knows how long.
Yikes! :behead: I shudder to think what could have happened if you had needed to use the fire handle.
 
My father related a story about a PBM - during a factory checkout they discovered that the feather actuators got crossed. Pulling both mixture and feather on one engine resulted in a very quiet couple of minutes. They did it twice, then got it fixed before delivery.
 
Would you care to elaborate on this? Differing points of view can be instructive. I like the both position for ease of maintaining balance as well as avoiding issues of unporting as described above. I can always choose to just use left or right, but can never use both if it isn't there. It is important to use either left or right when mooring a seaplane or parking sideways on a hill.
When the valve is in the off position are the tanks interconnected?
 
When the valve is in the off position are the tanks interconnected?
The system which has the left, right, both and off positions on the fuel selector valve connects both tanks in both the both and off positions. Remember that the label on the selector valve tells you which tank(s) feed the engine. The label tells you which tank combination feeds the line which penetrates the firewall, only.

The answer to your question is YES.
 
Cub left vent.jpg
Discovered that my left header tank vent line isn't plumbed per the Piper drawing as was suggested earlier in this thread. The header vent line comes in from the top of the photo into a brass T fitting on the upper fuel sight, the line exiting the right side of the photo is the upper sight line going back to the left main tank. This set up is how the right side is vented per the Piper drawing, in theory it should work just the same on the left side. Still need to check vent line for blockage. At least the timing of this is good, annual is due soon and panels need to come off and work done anyway.
 

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Found the culprit...a completely clogged header tank vent line. It looked like clay, I guess a bug must have gotten in some how. After draining the entire fuel system I removed the header tank and discovered it was still full...that's when I disconnected the vent line and discovered the blockage. My conclusion is that during the slip the left main tank unported and the header tank did not flow due to vacuum blockage of the vent line, thus leading to fuel starvation. I removed and replaced the vent line with new. Thanks to all for helping me solve the mystery.
 
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