This has always been a problem with my Super Tigre GS 40 in my TopFlight Contender. Engine at take off is sloppy rich and stays this way until maybe 5-7 minutes of flying. The engine then starts leaning itself out. I'll then have to land as sometimes it goes so lean it dies. I do indeed think the tank centerline is ever so slightly lower than the needle valve. Would this be causing this problem? I don't have the room to raise the tank, so is there anything else I can do to solve the problem? Would a regulator and check valve on the pressure line help? Just to make sure I wasn't running out of fuel, I connected the pump and sucked several onces of fuel out, so this problem is showing up way before it's out of fuel. Engine is fresh with a new ring and bearings from sitting and rusting. I was trying to break it in rich, but the thing keeps leaning on me midflight.

Mike

i bet it isn't broken in totaly. mine took about a gallon before it would hold consistent needle settings. check the needle where the threads are exposed just to make sure it is not leaking. i had to put a little piece of fuel tubing there.

How did you determine the needle valve was leaking on yours? I noticed mine is somwhat wet with fuel, but I don't know if it's from leaking or from when I pulled the fuel line off the nipple to empty the tank. The fuel tubing idea is a good one. I think I'll try that just to make sure it's not leaking. This engine, even when new, did the same thing. I thought it was worn out, but now it's been repaired and the symptom is still there. I know it's probably not broken in (ring not seated yet), so I'll keep running it way rich. If I keep the flights under 5 minutes, it's fine....but that's no fun.

MIke

Mike,


It looks to be a fuel system problem.
Please inspect the clunk line inside the tank.

The engine can become lean when there is a pinhole in that fuel line. as the fuel level goes down, part of that line becomes exposed to air inside the tank, effectively leaning the mixture.

Also, is your fuel tank completely isolated from vibrations?
If any part of it is in direct contact with the air-frame, the fuel will foam, with the same results...

Make sure there is a 1/4" of latex foam, between the tank and all adjacent parts of the tank compartment, including the brass/aluminium fuel tubes that exit the tank.

I did completely replace all fuel lines (inside the tank, and out) before this flight. I also added foam rubber around the tank on all sides but the top. Can't think what else would be leaning it out. I'll put some more rich flights on it to break in the new ring and see if this problem continues.

MIke

MIke,


With any and all engines I had run, the mixture strength changes only a little, between full tank and empty.
no more than three clicks of the needle are needed to compensate for that.

Do you happen to have your ST.40 inverted and fully enclosed inside that nice cowl the Contender has?
I had the .40 model and selected to mount the engine upright, under the wood mounting beams, to get the carburettor and the fuel tank center-line at the same level.

If you have it cowled, make sure there is sufficient air intake and at least twice as much exit area AND that the air actually flows around the head and cylinder fins.
That is in case your engine is simply over-heating, with effects similar to a lean condition.

This is a ringed engine and its piston-ring will not tolerate too many lean-runs.

Nope, I have it mounted upright, like yours, but on top of the rails. I just may have to relocate it to the underside of the rails if possible. Here's a pic of it ready to fly. Just to clarify, it didn't run lean on me to the point that it quit. Once i heard the engine break into the clean two-stroke sound, I throttled back and landing. I have the idle set so it's a 4-stroke idle, plenty of fuel. I never thought of mounting the engine under the engine rails. I'll see if that will work. I'm running a Sullivan 8 ounce tank with my ST GS40.

Mike

my needle valve was wet with fuel-the threads . one day i was at the field and could not get it to hold a setting. my friend notice the fuel, wasn't really a whole lot, and suggested a piece of fuel tubing. tried it and it worked!

today I put in two short 5 minute flights and it was fine. The only time I heard any leaning out was during loops and other high G maneuvers, but it only broke into the clean 2-cycle sound for a second. I did put some fuel line over the needle just in case it was leaking, maybe that was the culprit... I didn't have the nerve to fly longer and possibly have it flame out. Our field is narrow and today there was a viscous crosswind.

Mike

Dar Zeelon, does engine overheating have similar effects on the engine as a lean run?

I got a parkfly type with an AP 0.09 and i have recently put a pipe on to replace a long cardboard tube that i made, so the exhaust passes the radio equipment and does not accumulate at the front. I think it could be running hotter and it seems to be happy on the ground but when after i hand launch it, it does not seem happy and i have to land.

Anyway i didn't know that. What are the visible effects of it being overheated. Can you still see a trail of whiteish smoke from the exhaust (castor comming out)?

I also had a similar problem with a la 40 on a trainer that seemed to quit for no reason at about 6 mins in flight. So maybe this problem was related to the amount of fuel in the tank. Im not sure that it quit for being too lean though. The problem was resolved by replacing the fuel lines and checking all things to do with the engine and fuel suppy.

RTang, they are one and the same.

When the mixture is set too lean, the engine still gets sufficient lubrication.

The leaner fuel mixture ignites sooner and burns more quickly. As a result, the maximum pressure is reached before the piston reaches TDC and as a consequential result, more heat is absorbed by the piston (faster) and cylinder, the piston expands more and contacts the sleeve. The engine heats up still more.

If you are lucky, the engine will stop immediately, if not, this could be the end of its life.


When the engine gets insufficient cooling, the ignition and burn processes also happen faster, like with too lean a mixture...

Both could have the same result.


The most profound effect of the needle is not on fuel consumption, but on ignition timing.


ABC engines can survive a lean-run.

A ringed engine will most likely need a re-ring, if a lean run is prolonged.


I had an FP that did the same; leaned-out and quit after a few minutes.
It stopped doing it and began to behave normally, after the sleeve's nickel coating pealed partially...

Is your prop ballanced and do you have a fuel filter? If you dont i think its because of the fuel foaming

good catch on the fuel foaming. take and give a couple of shots of Armorall in the gallon of fuel. that will take care of the foaming. don't know why i works, but it does. let us know what happens.

How much Amorall and does is there any negatives with this? I use Cool Power 15% nitro and I noticed that on the label it says it contains some anti-foaming agents.

Also, is it normal for the engine to lean a bit during loops and other high G situations?

MIke

it's normal to lean in loops- do 4 to 5 in a row and see how the engine responds. no negatives- Clarence Lee from RCM also stated that. i run morgan's fuel to and it says the same thing. take your fuel jug and shake it. see it foam? now take and squirt some armorall in there and reshake. no foam right? i've been doing this for years and have had no problems. whenever i open a new jug of fuel, this gets done first thing. how many tanks of fuel (on the ground) have you run through it since you freshened it up?

MRBigg,


Isn't Armor-all silicone based?

If so, it is going to gradually coat the platinum glow element in your plug and there will be no possible contact, between the methanol in the fuel and the platinum catalyst.

No direct contact is no catalytic action, which means the element will eventually not retain its glow and your engine will just shut off, as soon as the glow battery is removed.

...And then you would say the glow plug is lousy...

Use only proprietary, non-silicone anti-foaming agents; like those used by glow fuel manufacturers; not Armor-all.

Dar, been doing this for years and have never had a problem- planes or cars. then again i don't use cheap glow plugs. it's pretty obvious that the anti-foaming agent Morgan uses doesn't work, just shake a gallon of it and see for yourself. then add the Armorall and watch the foam disappear. the amount added to a gallon is minimal, that is why i can't understand why it works so good.

DarZeelon, thanks very much for the insight on the lean run and engine overheating. I did replace the diverter with a different design and it works but i better not get off topic on this thread discussion.

I ran two tanks through it on the ground and so far three approximately 6 minute flights (about 5 ounces consumed per flight), all sloppy rich. In fact it was so rich it barely got off the ground (grass field didn't help either). Maybe it's in my head, but the compression seems to be increasing with use so I guess the ring is starting to seat. I may start gradually leaning it out as I get more time on it. Amorall is something I'll try too after I research how much to add to my remaining half gallon of fuel.

MIke

just give it a couple of squirts. if i were you, i'd run 2 to 4 more tanks through it on the ground. better off spending the money on the fuel then on a new plane because of a bad timing flameout.

OK after some testing this is what I'm finding. Today I took the tank hatch off so I could listen how the engine was running while I could see the fuel level. Sure enough, yet very gradually, the engine slowly leans out. This is at full throttle with the plane level on the ground. I stood there and watched as a whole tank was burned. Started it and tuned it to a VERY rich setting. Stayed the same until about 1/4 tank (tank is 8 ounces), then it gradually started breaking into the 2 stroke sound and picking up a lot of rpms. Evenutally in the next minute it continued to gain rpms and completely break into the clean 2 stoke sound, no more burbling 4-cycling sound at all. It eventually ran completely out of gas. Absolutely NO foaming of the fuel is occuring here, none, so I know that's not the problem.
Now without touching the needle valve, I fueled up another full tank and started it. The result? It's back to the burbling stumblin rich setting, probably several thousand rpm lower than the end of the previous tank. Letting it burn another tank repeated the results of slowly leaning.

Question:
Can it really be that sensitive to fuel tank position? I noticed that the tank center line is indeed about 1/2 inch lower than the needle valve. I'm guessing this is the problem as nothing else is as obvious. All fuel lines are new, inside and outside the tank, so it's not sucking air. This sucks because now in order to have a longer flight, I'd have to richen it to the point where it's barely got enough thrust to take off to compensate for how drastically lean it will get by flight's end. I may just try to mount the engine underneath the rails instead of on top. This will lower the engine. What do you think?

Mike

Mike,

My experience is that 1/2” is OK on a 40 with an eight-ounce tank.

If the engine were mine I would take it out of the airplane and bench run it with a different tank. The purpose for bench running would be to check slightly different tank positions and maybe discover anything else that might be strange. For cautionary reasons I would take the high speed needle out make sure the fuel entrance is absolutely clean. In addition I would run a 10 X 6 prop until the problem is solved.

The problem can be found but it seems like it requires an infinite amount of patience sometimes.

Taking off rich will eventually bring about the disaster we all like to avoid.

Bill

Bill,
Good idea about bench testing. I just happen to have a brand new 8 ounce tank that I could experiement with. This engine did this even when brand new in this plane. I attributed it to it being a poor quality engine, but so many people here like the GS40 and don't seem to have similar problems. I only have a 10x7 for this engine. Is a 10x6 better for breaking in? LEss load?

MIke

yep, less losd.

My charts indicate 10 X 6 for a 40 engine. Some people will run bigger props after break in. For break in and trouble shooting I prefer the engine run freely and not under heavy load. In addition heaver loads aggravate the problem that you describe. All of my 45’s fly epoxy heavy airplanes better with a 10 X 6 prop.

After the problem is solved a prop can be selected to fit your flying style and airplane characteristics.

Experience getting off the ground too slow has never been pretty for me so it is important for the engine running properly.

You will find the problem.

Bill