smh20502

My Feedback: (1)

As the title indicates, the engine quits half tank.

This engine is in a Seagull Edge 540, if it makes a difference.

The engine hasn't past what I would call break-in yet but it runs OK considering the bearings and ring were just replaced. I've got maybe 3 tanks through it on a 15/8. The last half tank it was running well, smooth throttle holding ok RPM and idle was acceptable. Put a 14/8 on there and it ran better, throttle was much smother and seemed to have more thrust.

With all the "Tuning" I've done, the only consistent issue I can't get rid of is it quitting on half tank. So it's a plumbing issue right? Where do I start? I just replaced the tank and tubing so maybe I had a leak somewhere. But if that were the case I'd think I'd have trouble tuning.

any suggestions as to what problem may be?

earlwb

Sure sounds like you have a hole in the fuel line inside the fuel tank. Or the clunk is stuck at the front of the tank. You can check by seeing if the engine will run with a 1/4 full tank or not. Naturally you'll have to pull the fuel tank out to check it. What happens is as the fuel tank empties the hole in the fuel becomes exposed and the engine leans out and dies on you. More than likely it is right at where the fuel line slips over the inside length of the brass tube going through the stopper.

The other possibility is you are running the engine too lean and as the fuel tank empties it leans out too far and dies. You can check that also by adjusting the engine to run on a 1/4 tank of fuel, then stop the engine, fill up the fuel tank, and you'll be good to go then. Also with 1/4 tank of fuel hold the nose of the plane up to make sure it doesn't lean out in a nose high attitude too.

smh20502

My Feedback: (1)

didn't think of leaning being an issue. Thanks for the 1/4 tank info. I'll be testing either tomorrow night or Sunday and use that to see where I am.

Hopefully the replacement tank and lines will do. Though now that I think about it, the pressure line is re-used.

NikolayTT

This has been my 'main' engine for about 9 years and it is a 'bit' special one. Is it overheating and then the leakig comes from the mufler ? What fuel is in use - no more than 10% does any good. The 15/8 popeller is a way too 'heavy' for this engine; try 13x8 or 14x6; best result I got with 13x7. Cheers, Nick.

acdii

I have an OS 52 in a Kadet and found that at half tank the motor would quit, or run like crap. Turned out the clunk was at the front of the tank. DOH!

SeamusG

You can check for a free and clear clunk by holding the plane upright (not running) and moving it side to side. You will hear the clunk hitting the sides of the tank. Uh, easier to do before you assemble the plane at the field - without wing and without fuel. Or when your buddies aren't reving their engines within 10 feet of ya.

smh20502

My Feedback: (1)

Thanks guys for the info.

Update- Got the engine to run below half tank yesterday. I had replaced everything, tank, lines, clunk...

now I have another issue. When nose down, the engine quits. Could be as simple as the pickup line not sliding to the front of the tank but I just don't know...any ideas?

earlwb

Yeah that sure sounds like the clunk is staying to the back of the fuel tank on you.  That has always been a major pain trying to find some of that extra thin silicon fuel tubing to use in the fuel tanks. There is someone who still makes the stuff, but I forget at the moment where I saw it being sold. Of course one has to be even more careful assembling a fuel tank using the thin fuel tubing as it is more fragile. The other somewhat more practical solution is to use a extra heavy clunk or add weight to the existing clunk to make it more heavy.

smh20502

My Feedback: (1)

Thanks for the reply.

The fuel tubing I'm using is the black neoprene stuff from Hayes, think Duo Bro has some too.

I like the idea of a heaver clunk. I'll look at it this week and see what I can do. It may be that the line is too long. I'm used to heli setup with a larger tank so this may be just user error.

earlwb

Yes the black neoprene rubber tubing is quite stiff and it gets more stiff over time too.
Your best bet is to get the silicon fuel tubing and use it, as it is more flexible and tends to stay that way for a long time too.

smh20502

My Feedback: (1)

Stiff? Then you may be thinking of different tubing. My stuff is more flexible than silicon or other fuel tubing I've tried. Have been using it in a nitro bird for a couple years with no issues.

You know, know that I think about it, maybe the tube is flexing but it's so soft it could be kinking...something to check for later.

earlwb

Oh, OK, I thought you were using the thicker stuff that isn't as flexible.
Yeah it just might be kinking on you.

acdii

If you are holding the plane and point the nose down at 45* or so it will quit. I was doing the same testing and the engine would quit as air got sucked up, Turns out that it was fine, I forgot to factor in the Gforces that force the fuel to the rear of the tank in a dive.   Since I know the clunk in mine can fall forward, I no longer worry about it, but now check to make sure it is at the back like it is supposed to before I fly.

jaka

Hi!
Most likely you run it too lean! That's easy to do as you run a too big prop! (15x8)!
The props to use is 13x8, 14x6 15x4W or 16x4W all APC.

Second ! When you hold the engine down it's going to stop. That's natural as the fuel pick-up cannot get fuel in that position for more than a few seconds.

It's a missunderstanding that the fuel tubing should be able to bend forward and follow the fuel ! -It should not be able to do that! The fuel tubing inide the tank should just be so long as it sits aprx half or one centimeter from the rear tank wall. And I repeat! The fuel tubing inside the tank should not be so flexible that it can bend forward!!!!!

MetallicaJunkie

as the tank level drops the carb has a harder time drawing fuel, you might need to open the needle a bit either that or a plumbing issue

blw

My Feedback: (3)

You can cut the fuel pick up line in the tank in the middle and connect them back together with copper tubing. This helps prevent the clunk from bending and going to the front of the tank.

A lot of people seem to overlook the condition of the vent line from the muffler. Fuel tubing can begin to soften up on the inside, and a little pressure mixed with heat will cause the inner tubing to collapse. I've seen fuel tubing do this with fuel cans too. They just stop pumping until you replace the fuel line.

freakingfast

My Feedback: (3)

I totally miss that, good catch NikolayTT & jaka! Yeah, that's a bit much. He could have gotten away with it when he was rich and breaking in, but when he tries to lean and add to that warmer weather, that could be the last straw. Once the engine gets heat saturated and the tank level is lower.... flame out.

Put less prop on it (less than 14X8) and I'd block off the opening in the cowl, opposite the cylinder too. A flat black painted, form fitted thin balsa sheet angled/recessed about 3/8" back in the opening, wont look bad. He could also take the cowl off for testing.

rcjetflyer0718-RCU

My Feedback: (1)

Another problem with the 91FX was the remote needle being part of the backplate and transferring heat causing bubbles and engine dying. The fix was to grind off valve housing and replace with OS 65LA needle assy and bracket.

smh20502

My Feedback: (1)

Crap, I'll have to look at what I've got. I have 2 or 3 of these engines and from what I recall, they are all converted or v2. Does it have a little metal standoff bracket and maybe a plastic case attached? I know I have one that is like that but don't remember if it's in this plane or in a box.

rcjetflyer0718-RCU

My Feedback: (1)

yes but the the bracket has to be from a 65LA the others 40-46 are too small.

smh20502

My Feedback: (1)

Ok, just looked. One in the box is the newer one the one in the plane is the older one. I guess I'll see how the plane runs this weekend. Wish I could fly but both fields I fly at have heli fun flies this weekend and I'm too busy at work now. If I can't get it the way I want, I'll swap engines...let this one be the backup.

TimBle

I've ben having similar flame out issues with my .91FX. Also been running a 15x8 MAS and after about 4-5min of flight it would ust bog down and die.
tried everything; replaced fuel lines, checked tank. It changed nothing. tried re tuning the engine, still consistent deadstick (lotsofpractice has mademe very good at this now )

then I recalled I am using a tank of fuel thts been open for about a year. When fresh it had 10% nitro (Coolpower) and the engine handled  OS #F easily with the 15x8MAS.
Light bulb went on and I changed the plug back to a OS #8 and viola! It runs reliable again. It seems to run the #F with the 15x8 MAS on the .91FX you need the 10% nitro minimum.

This is one of the most sensitive engines to tuning I own so it's constant work keeping it running reliably.
I hink a 14x8, fresh 10%NItro minimum Methanol fuel and a # plug is a good combo but burn throigh that can of fuel quickly.