7EC Fuel Shutoff Valve Leak and Engine Stumbling

jdhardin · Post by **jdhardin** » Tue Jan 08, 2008 22:30

Recently the engine on my 7EC "stumbled" in cruise. The stumble was a short, but attention getting drop of several hundred RPM that lasted for 3-5 seconds. The conditions weren't right for it to have been carb ice (80 deg day, cruise power, low humidity). After the power came back up I did a mag check and saw about a 400 RPM drop on the right mag. I discovered a problem with the harness on that side, and I've since replaced both harnesses. A runup and short flight showed normal RPM drops on both mags. But while working on the harnesses, I noticed I've developed a pretty bad leak from my fuel shutoff valve, and I'm wondering if that might be part of the stumbling problem. It also made a bit of a mess in the cockpit until I got a bucket under it. The valve is shown below:

Click to Enlarge

I have no idea what the part number is on this valve, but one of Bill Pancake's technical notes mentions wear in Champ fuel shutoff valves possibly starving the engine for fuel.

The questions are:
1) Does anyone know what the part number of this valve is?
2) Since the valve is leaking, could the valve be drawing air and causing the engine to stumble?
3) What's involved in removing and rebuilding the valve? I have two 13 gallon wing tanks, and I assume I have to drain all of the fuel, and I'm not sure the best way to do that.
4) Is there a replacement for this valve? I assume there isn't, because all of the threads I've read here mention there is no replacement for these valves, but not knowing the part number, I can't be sure.

And by the way, I'm not an A&P, so I'll either be doing the work under my A&P/IA's supervision, or I'll have him do it, I'd just like to know what's required.

Sorry for the long post, but the stumbling issue has scared me into making sure I cover all the bases.

marklamon · Post by **marklamon** » Tue Jan 08, 2008 23:20

Jay, I would say that the fuel valve would not make it stumble unless there is a blockage. With the fuel in the wings there is enough pressure to over come a small leak that is shown. The blue stain says to me that it hs been leaking for more than the past few flights.
Most all fuel valves can be repaired. The consumable parts would be an "O" ring and a flat paper washer.
The best/fastest way to drain the system is to turn off the fuel valve, disconnect the fuel line from the carb, turn the fuel back on and fill up 5 gallon cans with the stream coming out of the fuel line. This will also give you a good idea of your fuel flow.

After your done draining. you do not need to remove the fuel valve to fix it. But the bottom threaded fitting in your pic appears to be leaking also. Might be just the photo. Anyway you remove the linkage to the "On/Off" handle, then you remove a packing nut and the inards of the fuel valve will come out.

Clean everything and put some fine valve lapping compound on the tapered wedge, put it back in the hole and lap (spin back and fourth) a few times to reseat it. Lube it up with fuel valve lube (aircraft spruce) http://www.aircraftspruce.com/catalog/c ... rnlube.php The flat paper washer should be under the packing nut and the "O" ring should be on the smaller part of the stem.

American Champion should have all of the parts for the fuel valve.

Mark

jdhardin · Post by **jdhardin** » Wed Jan 09, 2008 00:04

Thanks Mark, that's good information! I really didn't think a leak like that could cause it to stumble, but I'm looking behind every bush right now. And you're probably right about how long it's been leaking - I've smelled a faint fuel smell in the cockpit for as long as I've owned the airplane (6 years), but I didn't see any leak on the valve at the last annual. I'm thinking it's probably been a very small leak for a long time, and something gave way during our recent freezing weather and made it unmistakable.

By your description then, I should just need to get the paper washer and O-ring from ACA? Any idea what the part numbers are, or should I just call ACA?

marklamon · Post by **marklamon** » Wed Jan 09, 2008 00:25

Jay, I looked in the book and the only numbers I found are 1-2403-1 and 1-2403-2. These are numbers for the fuel valve itself. It may help you when talking to American Champion. Also there might be a little spring in the fuel valve either under the wedge/taper or on the stem of the valve. Mark

Here is the only pic I could find on the net of a fuel valve. Yours has 3 maybe 4 parts. This on is from a DC-3, but I wanted to show you what the wedge looking piece looks like.

jdhardin · Post by **jdhardin** » Wed Jan 09, 2008 01:03

Thanks again Mark. I just sent ACA's parts department an email before I saw the two part numbers you came up with. I sent them my photo, so I'll see what they say.

Dennis · Post by **Dennis** » Wed Jan 09, 2008 13:00

Jay,

I have a chart which shows the potential of carb icing under different ambient conditions. The best conditions for icing at cruse power is between 60F and 90F ambient temperature AND @ 60 to 70F Dew Point with the relative humidity from 40% to 100%.

The best opportunity for icing at glide and cruise power is between 88F and 105F ambient temperature AND @ 50 to 70F Dew Point with the relative humidity from 20% to 40%.

This is because there is a pressure change across the venturi in the carb which results in a significant temp drop at the carb venturi. So, bottom line, you may have indeed had a little carb ice.

Good luck with your search, Dennis

Paul Agaliotis · Post by **Paul Agaliotis** » Wed Jan 09, 2008 13:29

Jay,
The fuel valve was made by Imperial Brass. The valve has not been in production for some time. After the John Denver crash off Monterey I think production of all valves stopped.
I have found two styles of the Aeronca style valves. The exit is tapped for either 1/4NPT or a straight tube thread. In the past I have found leaky valves that had pipe thread fittings installed in the tube thread valves. The thread pitch is close enough to allow the mix-up.
Just a little information when you remove your valve.
Paul

jdhardin · Post by **jdhardin** » Wed Jan 09, 2008 20:53

Thanks for all the info guys.

Dennis - I have the carb icing probability chart myself, and based on the conditions, I think it was extremely unlikely. It shows that the probability of carb icing was about the same as it would have been in cruise on a 100 deg day with 20% relative humidity. If carbs were icing up under conditions like these, we'd have to wire the carb heat on all the time. I'm not saying it absolutely couldn't have been icing, I just think the probability is very low. I certainly had a problem with my ignition harness, and that may well be all there was to it. I've also thought of the possibility of a sticking exhaust valve.

Thanks again for the information.