moparcolt

My Feedback: (2)

[>:] I have a Sig Kadet LT-40 ARF which has been a great plane, except, It keeps stalling/cutting out at approx. 1/2 tank of fuel. I put a bigger tank in the plane 14oz. and for some reason it just dies at 1/2 tank, It will restart but won't stay running long unless I refuel it again. what is up here. do I need to put a pump on it or is there some other problem? I checked the Rpm's and it seems OK about 11,100 at WOT.
It will cut out at any rpm Idle, 1/2 ,WOT it doesn't seem to matter.

The tank is in the stock locationand the motor mount is in the stock location nothing has been altered, except the fact that it has a 4-stroke motor on it.

Could it just be that the carb is out of adjustment?

Please help it is driving me INSANE!!!!!!

bigchap

you have to check that the spraybar on the carb is either level with the tank fuel outlet [ideal] or a max of 15mm above, you should also check that the tank clunk is not caught up,have you had a heavy landing lately?,such an event would cause a clunk problem.

phread59

It sounds like a klunk problem in the fuel tank. I would look to see if the klunk is getting to the bottom of the tank. It may be hitting the back of the tank and starving it for fuel. Also check the stopper. You may have a leak in the stopper somewhere allowing air in. My 50 with a 12 oz tank will run it dry in my Senior. I would look at the tank and lines real closely. Good luck on finding this irratating problem.

Mark Shuman

jaka

Hi!
It's simple ! You have a too large fueltank!!!
Put in a 6oz -8oz tank instead and see the difference!

The problem is that our modelengines have difficulties to cope with the different fuelpressures that takes place when the tank is full and later when the tank empties.
At first when the tank is full the fuel pressure is high and the carb setting is adjusted to this which means the engine runs good.
Later when the tank empties the pressure gets less and the engine is having difficulties sucking fuel....remember you haven't changed the carb setting because the airplane have been up in the air............if the fuelpressure gets too low (or the highspeed setting is too lean) the engine dies of fuel starvation due to lack of fuel.
The only way to overcome this ..using the big tank you have is to set the highspeed needle extremly rich when the tank is full and hope the plane will take off at this setting ....and still run when when you are about to land the airplane..or which is better ... to use a 6-8 oz tank and enyoy the 12-15 minutes of flying time this will give you!

Regards!
Jan K
Sweden

DBCherry

My Feedback: (4)

Interesting thought Jan k.

But wouldn't the fact that the muffler is pressurizing the fuel tank keep the pressure fairly equal throughout the run?

As was mentioned, I'd check the clunk first. If it's hung up on the back of the tank it may not get fuel once the level falls below half.

A hole in the tank, stopper, or a line could also introduce enough air, once you reach the half full mark, to lean the engine to the quitting point.

I'd also check the muffler pressure fitting. If it's clogged you might not be getting adequate pressure to the tank.

Or as Jan k said, it may just be an issue with tank size.

I hope you figure this out. And if/when you do, please let us know what the problem was.
Dennis-

siclick33

One of the main reasons ducted fan fliers use in-flight needles is to counteract the change in mixture as the fuel is used up. Some people suggest setting the needle with 1/3 to half tank so that optimum mixture occurs as you come to the landing phase.

I don't know if this will help you though.

A 14oz tank with a 4 stroker. Are you going for an endurance record? LOL

moparcolt

My Feedback: (2)

well, I think that readjusting the carb with the tank 1/2 full would fix the problem and it would then run the rest of the tank out, but it don't. It just doesn't want to run for more than a 30 seconds when the tank gets low, in the air on the ground it doesn't seem to care. I changed the lines and checked the clunk they seem ok. I'll have to check the tank placement, and look into the muffler thing. I have anothr muffler (brand new) I might put it on and try that. thanks soo much for the input!!!!

bhole74

Have you checked for air bubbles in the fuel line? If there are, you have a leak somewhere. If not, I would say it's a pressure problem. I would try a smaller tank as well.

jaka

Hi!
Pressure from the silencer could no fix this! Sorry!
What I said about tank sizes and pressure changes is a is well known fact if you have been into this hobby /sport for as long as I have....sorry doesn't want to put myself on any high horses ....don't like that...!
Regrads!
Jan K
Sweden

Rodney

Most probably a fuel line problem inside the tank. Probably a hole right at the stopper between the clunk and stopper. Replumb the inside of the tank and your problems will most likely dissappear. I've never had a problem with that size tank so, unless your tank is mounted a long way aft of the firewall, size should not be a problem. Be sure to use large enough fuel line.

SST

My Feedback: (2)

I'll bet it's a pinhole in the line that allows air in after the fuel level lowers enough to expose it. I agree with Rodney...Re-plumb your tank and I'll bet you have no more problems.

moparcolt

My Feedback: (2)

I was thinking about this all day and I am thinking the same thing there has to be a pin hole in a line inside the tank causing it to suck air and stall. Or possibly ,and this is not as likely, since the stopper is on the front of the tank at an angle it could be sucking air around the stopper. when the level drops below that it would also cause the same problem. I probably won't get to it for a few days, We'll see then!!!!!!!!!!!!

Phoenix57

Just a thought here. A friend of mine had exactly the same problem. We tried everything we could think of. Finally we raised the fuel tank about a 1/2 inch and problem solved. We think it had to do with the amount of pressure required to push the fuel to the engine. The higher the tank the less pressure required. Hope this helps.

moparcolt

My Feedback: (2)

Well, I shortened up the hose going to the clunk, it wasn't moving as freely as it should, it was touching the back of the tank. The tank is a 12oz. not a 14, I bought 2 that day and used them both the 14oz must be in the other plane. I was looking into raising the tank, but it is already against the top of the fuse. The outlet looks like it is just about level
with the center of the carb. I havn't fired it up yet because it is raining like crazy and I'm going to have to run almost a full tank through it to make sure all is well, and this is not something I can do in the basement. MaMa would have a fit!!!!!!!!![8D] so as soonas I get a break in the weather I'll see what happens.

moparcolt

My Feedback: (2)

I started the engine today, and it ran fine for about 2minutes and then quit which is a good thing because when I looked it over I noticed the line from he muffler to the tank had melted/burned through on the end where it connected to the preasure fitting that hose must have been worn out and not making a good seal as it warmed up and bleeding of preasure. I cut the line back a 1/2" put it back on and walah!!! ran the tank empty!!!!!!!!!!!!!
Would have never found that one, or not too quickly anyhow. The plane doesn't have that many flights on it I am suprised the hose gave out so quickly. I can't wait to see how it does at the field,it is supposed to be sunny and warm this weekend I can't wait.

Thanks for all your help guys
Chris