National Aeronca Association Bulletin Board

After installing a new carburetor last week, static run-up was about the same as with the old one; 2300 rpm with little or no change with leaning on the ground. Carb heat indicated a 150-rpm drop. Mag check at 1800 rpm was normal with about 100-rpm drop for the right and 75-rpm drop for the left. I positioned the mixture full rich for takeoff and cruise. Climb out was improved with 2400 indicated rpm and 500 fpm climb. Upon arriving at KBAZ (about 20 minutes into the flight) I executed a touch and go on runway 35. Carb heat was used during downwind, cross wind and final approach. After landing, carb heat was closed and the engine “coughed” during throttle advancement. Power and rpm was normal during the first 300 feet of the climb. Then abruptly the engine’s power declined significantly to about 2100 rpm and the plane failed to climb. The engine was running smooth and was not making any unusual noise. Oil pressure was 70 psi and oil temp was 180 degrees. I immediately lowered the nose and configured the plane for the best airspeed for landing. Before I had a chance to “play with” carb heat or mixture, the engine re-gained its full power. Total time of power loss was about 6 seconds. It felt real ugly – like it would stop running any second. I returned to the field with “power off” and landed uneventfully on runway 13.

I stopped the engine and made a full visual and functional inspection. Everything was normal. I restarted the engine and did a static run up. The engine was running “rough” indicating fowled plugs. I chipped the engine (ran full static rpm for 1 minute followed by a pump of gas from the primer. Note: the primer required about 6 strokes before it filled with gas to pump gas through primer tubing.). Max rpm was sluggish at 2150. Then I leaned the carb and rpm increased to better than “normal” - 2350”. With the engine leaned and chipped, it seemed to run well and develop normal power. We took off and climbed to 5,000 feet while circling the field before departing for Kestrel (1T7). The engine ran normally through out the remainder of the flight. At this point I felt I had determined the cause of the mystery power loss and had corrected it by proper leaning.

However, this was not to be the case. The next day I flew to KBAZ after “proper” leaning. The engine ran perfectly during climbout and cruise. After landing and executing a touch and go on runway 35, I again experienced a power loss at about 300 feet agl. This time I immediately pushed the mixture to full rich and the engine seemed to improve, but only for a few seconds. Then it lost power again and so I leaned it and the power returned. I “played around” with the mixture control to see if I could find the ideal position, but it did not seem to matter. I executed two more touch & goes and each time the engine hesitated and lost power during the climb at about 300 to 400 feet before turning crosswind. I came to a full stop and checked everything I could. Nothing was abnormal.

I spoke to Ron Fisher, my mechanic, about the problem and after advice from 3 experts (National Aeronca Association Discussion Forum), we concluded that the mal functioning primer might be the culprit, leaking air or fuel into the cylinders. Ron disabled the primer completely. I again took the Champion to KBAZ with high hopes that we had found the problem. Alas, upon the first climb out after touch & go, the engine went through its “resting” routine again for about 10 seconds dropping to 2100 rpm.

I have concluded that the only explanation left is a blocked fuel line (or plugged vent) or the carburetor itself. Carburetor icing does not seem to be plausible because the weather was clear with low humidity and temp of over 60 degrees. I faithfully used carburetor heat. I have ordered 2 new, vented gas caps to try first (The plane currently has one vented and one non-vented gas cap, with no explanation for why). Then if there continues to be any hesitation with the engine we will swap out the carburetor since it is still under warrantee.

Does this seem reasonable and do any of you have other explanations for the mystery loss of power on take off? By the way, both mags are brand new as are the plugs, cables, air-intake box and carburetor.

Thanks, Larry Miller

Larry,
It does seem like you're 'hot on the trail'. Fuel blockage is certainly a possibility and I had a tank vent problem one time when the AI made a new fuel cap gasket and plugged the cap vent. After about 15 minutes of flying the engine died on a takeoff (touch and go) run. Got our attention right away. I'm not sure exactly how your tanks are vented (I'm assuming you have two 13 gallons (?) but it bears looking into. I would think putting vented caps on should help, if that's the problem.

Good luck and let us know what you find out.

Mike

Have you grabbed the fuel shut off rod and twisted to make sure it is opening all the way? Had a similar situation with my champ and found the valve was only opening partway. Simple things first. New universals made a heck of a difference

As well believe you are on the right track. Jody's comment is valid as this has happened on several airplanes as well and would look there first, or even take the valve off and confirm that its really opening all the way.

Great idea about the shut off valve, because I had it off during the installation of the new carb and air intake box. Maybe it didnt turn on all the way. I will let you know.

I do have two 13 gallon tanks and they are not vented to the outside but are vented to each other. How do I know? I leaned over the wing and blew into each tank with the opposite cap on.

Thanks,

Larry

Larry,
The tanks need to be vented to the atmosphere at some point. I think I would do a static fuel flow test and see if the flow from the tanks is enough. This appears to be a serious problem and I would not recomend flying it until it is solved.
Paul

Thanks for the advice Paul.

I agree. I should not be taking chances until I figure this one out.

I will conduct a static test of fuel flow before taking the Champ up again.

Regards,

Larry

What kind of fuel have you been using? I've heard of fuel lines swelling because of AutoGas.
I think your on the right track, it sounds like a fuel supply problem or maybe an induction leak, but I dought that.
Good Luck!

nkh

A Few years ago, I upgraded from my O-290D2 to an O-320. At takeoff power, after 2 or 3 minutes, the engone would start to lose power, and showed all signs of being too lean. After a lot of work (changed carburetor, fuel caps, etc.) I finally pulled off a flex hose coupling from between two aluminum fuel lines. The inside diameter was swolen down to about 1/2 of what it should have been. Changing the hoses fixed my problem.

That's from a topic about av-vs-atuo gas on supercub.org. Apperantly auto gas has trace amounts of alcohol, MEK and some other nasty stuff to reak hell on flexable hoses.

nkh

Larryjmillermd:If you are running wing tanks only, run forward facing vent tubes. Normal caps will be in low pressure area of wing and may not allow fuel to flow at a constant rate. It will at first, then it will slow down the flow rate enough to make the engine run lean and eventually quit.
Ron

Ron,

Now you really have me worried. I have only 2 wing tanks, each holding 13 gallons. The tanks are not vented, except between the two tanks. There is no outside venting. How do I know? I can add pressure to one tank with the opposite tank capped and the pressure remains high. No leak (venting). If I place a vented cap on the opposite tank and add pressure, the air escapes through the vent in the cap.

It makes sense what you are saying about the low pressure over the wing sucking air out of the tank during flight resulting in decreased flow. I checked with the previous owner and he flew the Champ a couple of years with the single vented cap without incident.

Did someone in the past cap off the factory vents for some reason? Were the tanks installed without vents? How can I add vents? Did mud-dobbers make a nest in the vents? Is there a way to find the original vents and clean them out? The only functioning vent to my two tanks is the vented cap on the right tank.

Also, why does Wag-aero continue to sell vented fuel caps for their replacement wing tanks (SKU: E-482-000)? Are they dangerous?

Thanks for any information you can give me.

Larry

Larry,
I think I would get a 7EC manual and check your installation. The 7ECA with the 13 gallon tanks use a vent line connected to the O/B side of the tanks with a ram air tube exiting from the R/H wing fairing on top.
The vented fuel caps used today will allow air to enter the tank as fuel is used but will not vent when presure is applied to the tank. I have had cases where the wing tanks were slow to transfer and the main tank fuel cap was the problem. The cap would not allow the displaced air to vent from the main tank as the aux fuel entered.
As far as W-- A--- goes I have never found any of their items to be of use on an aircraft. Any usable item will be manufactured by another company and they act as middle men. When the Safe Air inventory is gone so will the quality. I would not recomend them for aircraft replacement parts.
Paul

Larry see service letter #39.
The fuel caps should be unvented,cap # 1-8768-2. the vent should come up through the wing gap farring about two inches with a 90 degree bend forward,this will produce positive pressure in the tanks.
Doing a fuel flow test on the ground may prove satisfactory, but in flight with the negative pressure on top of the wings and a leakly fuel cap you may not get the proper fuel flow. were these tanks champion kit 192?

Give me a call on the telly and we will talk. 304-788-1974

I just got back into the country after 3 weeks in the Sea of Cortez.

You guys are awesome. I owe you big time.

I did a static fuel flow measurement. I was barely getting 1 gallon per 6 minutes. That is only 10 gallons per hour and on climb out the Lycoming 0235 uses 11 gallons per hour. I checked the shut off valve and sure enough it was not all the way open. When I did open it the fuel ran like a stud horse (a gallon in about 2 minutes). The universals are worn. When I opened it all the way it began to leak fuel into the cabin.

Since finding the problem – I have had no more loss of power on climb out.

Do any of you know where I can get a new fuel valve? Can I substitute a generic fuel valve?

Thanks again for helping me to solve a serious problem. I would never have thought of looking at that valve.

Best regards,

Larry

Larry,

Glad to hear that you found the issue and its so easy to take care of. Well, sorta of that is!

There is no direct replacement on the valve, but Carl (plain carl) on the fAA email list is working on a STC ball valve replacement for the Champ.

They are getting hard to find these days so overhauling them seems to be the only route at this time. People take them apart and lap the valve itself to keep them from leaking but not sure about the universals.

Anyone else have any sources for parts on this?

BTW, where were you in the Sea of Cortez? I used to scuba dive on Tiberon island, off of Guymas and for many years landed on the beaches of San Franciscito bay on the Western tip. Put a snorkel on and found beds of scallops about 100 meters off of the beach. A bit of lemon, butter and beer and we were happy campers!

Joe A