millertym2000

My Feedback: (4)

Ok, I have a OS 46ax that keeps dead sticking after about 2/3 of the tank has been ran through. I tried running it richer and then leaner but still the same. I changed all the feul lines thinking maybe a hole in a line and still the same. how high does the tank need to be mounted compared to the carb or needle intake? Do you think this could be what is causeing this engine to die? Its never really ran right, this is the only plane that its been on. Im thinking about moveing it to a different plane to try that.

mscic-RCU

My Feedback: (6)

If the fuel tank is mounted too low in the fuselage, it can cause this condition. Ideally, the center line of the fuel tank should be on the center line of the carb. If you are unable to achieve this, then you might consider a pump to provide constant fuel flow.

brett65

My Feedback: (18)

I have the outlet 1.5 inches lower than the carb in my trainer and its fine. Make sure your clunk is installed correctly and that it rests on the bottom of the tank. Some arf provided fuel line can be too stiff and if not used correctly then the clunk could ride too high in the tank.

Mr Cox

Could also be the clunk bouncing about and getting air into the fuel line when the level is lower, so check for bubbles in the line. The tank should only touch soft foam and not the airframe it self, you'll also need a well balanced prop to minimize vibrations.

rlipsett

when you changed fuel lines did you change the ones inside the tank?

millertym2000

My Feedback: (4)

Ok, The clunk is fine it is at the end of the tank and flexes to the bottom of the tank. I replaced the tank thinking this might help, so this is a new tank and new feul line. I checked the line for hole before I put it in the tank. The tank looks like the spray bar of the carb is in line with the top 1/4 of the tank. Any ideas would be great..

opjose

As Mr. Cox alluded to, it's "some other" problem...

ALL of our engines would die the second we pointed them straight up if the tank height was truely the issue people seem to make out it is around here.

Tank height primarily affects the plane while it is sitting on the ground, as fuel can siphon out of the carb, or back into the tank.

Once the engine is started, muffler pressure makes it a relatively small issue.


I've had what you describe occur, because I made my fuel tubing too long, within the tank.

The clunk would flip "up" during a roll or some other manouver and stick "high" in the tank while the plane was flying level.

Shortening the line fixed the problem.


Also when your tank is down to about 1/3, as in your case, you have to remember that during downlines air can get into the clunk & lines.

There is a myth about the "fuel sticking in the back of the tank" which is totally untrue...

At 1/3 tank, even a slight 20 degree dive can uncover the clunk. If this happens for more than a second or two, the resulting bubble will cause the engine to cut off.

You COULD attempt to richen the low end up to help keep the engine running through the fuel starvation... this often helps... but it will degrade idle a bit.

jetmech05

the 46 AX is a great engine...I have 3.....if always at 2/3 of a tank and you changed tanks then....it's either the height of the tank or muffler pressure....
try running the engine on the ground and see if you ever get air bubbles in the line before it dies....

brett65

My Feedback: (18)

I have heard this preached so much, but have never seen it happen in my planes. Both my trainer, stick, and extra's tanks are wedged in tight against the airframe, and they will all fly to a dry tank. I have to believe that either this was just a problem with older fuels or is basically a myth.

alfredbmor

I suggest solving the problem in a step by step fashion.
Firstly, try to fit the tank (the middle of the tank) accordingly with the spray bar.
If this is not solving the problem, then reset the idle needle valve and the HSNV, do not try to get the most of the engine, and just make it run rich. If you still have the problem (the engine dies when there is only 1/3 of fuel left in the tank) then, your engine is overheating because of a number of reasons (Cowling, old engine, bad fuel, still bad tuning etc.)

opjose

... ALL of our engines would die the second we pointed them straight up if the tank height was truely the issue people seem to make out it is around here.

brett65

My Feedback: (18)

I have to agree with opjose, the tank height argument is like the don't pop your knuckles argument. I believe fuel travel distance would have a bigger influence than relative height.

millertym2000

My Feedback: (4)

Ok. The clunk moves freely and does not hang up. The tank is a little lower then what they say it should be but It sounds like that shoudn't matter. This plane ran fine with a 46la in it and now with this 46ax it keeps deadsticking. I 'm going to run a tank of feul with it on the ground and see if it still dies. This engine has started and ran fine out of the box till it gets in the air and runs about 1/2 to 3/4 of the tank out and then dead.

opjose

Fill the tank about 1/2 full then perform nose up and nose down tests.

Nose up the engine should continue to run through all throttle positions.


Nose down tends to be problematic, as often the clunk gets uncovered.



We tend NOT to let the clunk travel forward with the fuel, which has repercussions...


Unforuntately because if this the clunk can become exposed when you run with 1/2 tank or less in a nose down attitude.


Watch the fuel tubing as you run the engine nose down. Look for air in the lines.


The ideal situation is of course that the engine continues to run and idle through all attitudes for any length of time up to an empty tank.




Also remember that in the air the engine runs leaner than on the ground...

Couple this with an occasional air bubble, and you can get unwanted deadsticks.

millertym2000

My Feedback: (4)

thanks opjose for the info. I'm going to run it through the test tomorrow. I'm at work till in the morning. we work 24 hour shifts (EMT) . hopefully this will help figure something out.

millertym2000

My Feedback: (4)

Ok I put a 1/2 tank in the plane and ran it on the ground then at wot put it nose up and down and on its side ect.. and once it ran for a while it did die on me with the nose down and the clunk not getting any feul. I did notice that the engine mount screws on the left side were loose and the engine was loose to vibrate. I tighted those and then put a new prop ( the other was an old one with some knicks in it) I'm going to have to take it back up to see what it will do now.

opjose

Bare in mind that unless you go to a completely different type of tank/plumbing combo, there is little that can be done about fuel starvation ( other than richening the mixture even more ) once the tank has about 1/2 to 1/3 fuel remaining.

Some people use header tanks, or resort to bladder tanks to solve this problem.

It's plagued me to no end with my Funtana s90 until I went with a header tank.

42etus

My Feedback: (2)

This may not be a fuel problem at all. An engine that runs fine on the ground and ½ way through a flight, then suddenly quits, is a classic example of an engine overheating. Is this engine in a cowled plane? If so, it may not be getting enough air flow through the cowl, leading to overheating. Just my 2¢, YMMV.
Paul

CGRetired

My Feedback: (1)

This is all good information but one particular item has not yet been addressed. You never mentioned what aircraft this issue involves. If it's an ARF then I would seriously think that it is NOT tank position. Most ARF's are designed to have the tank centerline in line with the carb, or darn near it. The best situation is the shortest possible fuel lines, a properly installed fuel tank with foam protection from vibration, and a properly installed fuel feed line (inside the tank), clunk, and both vent and pressure lines. If you don't use a vent (two lines, one to the carb and one to the muffler pressure tap) and if they are as short as possible, and if the clunk is free to move as it needs to without getting stuck, then it could be an engine that simply needs to be run.

CGr

millertym2000

My Feedback: (4)

the tank is on a goldberg eagle (no cowl) The engine is fairly new probably less then a gallon through it. It sounds like it gets hot and dies but I've ran it rich, and it still does it. Its gotta be something to do with the engine because when the 46la was in it this never happened.

opjose

So true... even if you invert the engine the difference that results has VERY little effect on siphoning and NO effect on how the engine runs, contrary to what is often posted here.


Note however that with fuel levels less than 1/2 tank and especially by 1/3 tank or less, the tank WILL become uncovered during downlines, leading to air bubbles in the line, as he has directly seen with his nose down test...

Short of replumbing with a header tank, or a fuel bladder, or finding a way to PERMIT the clunk to travel forward, there is no real cure for this with a standard setup... often this somewhat "normal" condition is seen as a problem, especially with bigger engines.

With a smaller engine, we normally don't run the tank down to the point that this is a problem.

davo580

just wondering have you got the overflow/pressure tube bent the right way.. is it facing the top of the tank. I made a mistake one time and it was facing down and when i filled up the tank it only filled it about 3/4

opjose

Yup that will do it too, which is why the suggestion that he compare the difference between his old tank and his new one.

F4U Corsair

My Feedback: (22)

Interesting thread! I have a new OS46AX that I'm having the same issue with. My instructor can run it inverted and all wacky attitudes when the tank is 1/2 full or above, once he hands it to me and it gets to 1/3 tank it usually dies after either a dive or sharp bank. We have adjusted the low end several times, we are running on the rich side on the high end needle, engine is not hot when we checked it after the dead sticks or when landed before dying. We are checking for air leaks everywhere, tank, lines, pressure nipple, etc. I had the pressure line brass tube up tight against the tank bubble (sullivan 10 oz) so I bent it down a bit. He is thinking I may be having a tank pressure problem when the fuel gets low. I'll fly again on Sunday and report back if this helped.

If the clunk is not moving forward during a dive and is starving the engine, how do you correct this? Do you make the brass carb tube shorter allowing the fuel line/clunk to flex more and bend forward?

Odd that we both have fairly new OS AX engines and are having the same problem, I'll be following your efforts to resolve this as well. Good luck!

DG

TedMo

Ok I think perhaps you have stated what may be happening. Brass tube inside tank is too long not permitting the fuel line to flex sufficiently. Also that fuel line is a bit stiff? Try using a smaller diameter fuel line.