I have an Evolution 61. It has been in a Goldberg Chipmunk for the last 2 years and it ran great. This last fall the engine suddenly won't run while the plane is inclined and stalls out at vertical. It had never done this before. I have replaced all the fuel tubing as well as the fuel tank. I have bypassed the fuel dot. I am planning on changing out the needle valve and or the carb next.
Any other suggestions???

Thanks
John

And I am running a Bison Muffler. I've tried to use the original muffle but It won't fit.

A couple of questions. Did you richen the low speed needle valve yet? What throttle setting does it die out, 1/2 or full throttle? Did you replace the fuel line from the remote nv to the carb? It may be a good idea to pull off the carb and change the o ring.

I have not messed with the low speed setting. I am at WOT when it dies. Replaced the line from the NV to the carb. Rplacing O ring and or Carb was next on my list. Just didn't want to.

Did you readjust the main needle?
Usually as the weather changes, cold or warmer or really hot and humid, you need to tweak the needle a little to compensate. Cold air is more dense so the engine tends to run more lean and when it is warmer and the air is less dense.
it sounds like the engine was a little bit too lean.

Now if you have been flying regularly for the last two years, and have racked up a lot of hours on the engine, it may be worn inside and now doesn't draw fuel as well as before when it was newer. Compression can become reduced and it causes a reduction in the suction available on the intake part of the stroke of the engine. It is worth checking to ensure the bearings haven't warn (think seals on the front bearing) or the O-ring on the carb, or the gasket on the backplate. maybe one or all are at fault. The cylinder and piston being worn down more so you have less compression means you get less suction on the intake stroke to draw fuel into the engine, and less pressure to force the spent gasses out of the engine too.

The newer engines tend to use a sealed front bearing to reduce the messiness of a glow engine, but with sealed bearings the engine designer doesn't worry about crankshaft to crankcase fit, so if the seals go bad the engine can suck air in through the front bearing and also it pushes air/fuel out the front bearing too.

Oh yeah, do check the muffler vent fitting in case it got partially plugged up with old fuel and carbon, etc. A plugged vent fitting can cause poor fuel draw problems too.

Well that doesn't sound like the easy fit I was hoping for......

Thanks for all the info......

"Easy Fix"

richen the low end about an 8th of a turn, and tune the high end so that is is about 300 rpm lower than peak

From what I've seen, these engines from Evolution are tough and take a lot of hard use. I have a couple of smaller ones with a lot of time on them and it looks like they will last forever. As Earl said, they do wear some. You can turn the engine over by the prop and see if it has compression at the top. Are you using an OS 8 plug? If so, toss it and put in an A3 because all of these engines really need a hotter plug. You can do a quick check of the bearings by when the glow plug is out by turning it over and feeling for any rough spots, etc.

A lot of the advice you are getting is because it sounds like it is running too lean when you put the nose in the air. It's not a great test, but one everyone learns at some point. Earl is right about the muffler vent having an effect on it being too lean. Just out of curiosity, what prop are you using?

All the seals become hard and useless sooner or later.

Try replacing the seal of the needle valve or adding vacuum grease inside the valve assembly.

John, try this trick that many use when setting the high speed needle. With the engine at WOT (wide open throttle) hold the airplane with the nose straight up. If the engine sags then you are likely too lean and need to richen the needle a click or two, then try the same thing again. If it sags or quits again richen the needle more yet. If you can't get the engine to hold a WOT setting while holding the airplane straight up even after this, then you can proceed to look for other issues. Also has the glow plug been replaced recently? Let us know what you find.

Thanks for all the good info guys...
I haveen't had a chance to work on it since my last post....
I will keep you informed..

the above is the simplest and most common test. start the engine and let it warm up for a minute or so, then advance to full throttle and hold the aircraft steady and raise the nose into vertical position, if the motor gains rpm quickly and then dies, adjust high speed counter clockwise by 1/4 turm max. If those adjustment to not resolve the issues, then looking into the other above posts is recomended.

Quote:

ORIGINAL: motoman326

I have an Evolution .61. It has been in a Goldberg Chipmunk for the last 2 years and it ran great. This last fall the engine suddenly won't run while the plane is inclined and stalls out at vertical. It had never done this before. I have replaced all the fuel tubing as well as the fuel tank. I have bypassed the fuel dot. I am planning on changing out the needle valve and or the carb next.
Any other suggestions???

Guys,


This guy specifically wrote that the situation is new and that it had not been the case before.

So, there must have been a change that we all are overlooking somehow.
Most of the solutions given here will be helpful for a newbie, who is still not too keen in engine adjustments; but not for someone who has been flying this engine and model for a couple of years, without problems.


We must all look at what could have changed to cause this.

The OP wrote about replacing most of the external fuel-lines...
To me it seems like the problem could be a pin-hole in the pick-up tube, inside the fuel tank (which the OP did not mention replacing); which formed over time. The hole is near where this tube connects to the tank's exit nipple.
When the tank is full and the model is level, the hole is dunked in the fuel and has no effect.

But once the model is raised to nose-up the hole is exposed to air; and the engine goes lean as a result.



EDIT: Language.

Dar, you theory may be correct, but it may not, and all the clues have not been presented and thus so far we are simply taking it for granted that the HS adjustment is done correctly. He did not mention anything about HS needle adjustment to help in the diagnosis, such as "even when I set it obviously far too rich on the ground, it still quits in the vertical" or "I set it 500rpm back from peak, and when I hold the nose up and pin it, there are still a few rpm left when I give the fuel line a quick pinch" or "when I hold the nose up the rpm pick up a whole bunch or seems erratic" or anything to do with engine behaviour on the ground. Therefore it seems logical that people will bring up HS needle adjustment to eliminate the obvious first.

Sorry folks I should have mentioned that....
Yes I have backed out the needle valve in increments (first 1/4 turns and then 1/2 turns) after each adjustment I would raise the nose and still the engine would sputter and then quit at vertical. I eventually backed it out all the way and the needle valve came out (obviously I went too far that time.) I have also leaned it out in small increments just to make sure but no luck. I have also replaced the fuel pick up line in the tank as well as the tank itself and all of the external lines. I have bypassed the fuel dot (someone suggested that might be the culprit) but the problem persists. I have taken the engine off and am planning to run it on a test stand to see if I can duplicate the problem.
I am going to replace the glow plug as well. I have been running an 8 but will get an A3 as well to try.
After taking the engine off and turning it over by hand, it still has good compression and I can’t feel any rough spots. I will put on the stock muffler on the test stand as a test as well.

The next step after I put it on the test stand and the problem persists…Replacing the needle valve and the carburetor “O� rings.

Am I forgetting anything?

Thanks you all for your suggestions. The best one I have received so far is from a fellow club member. “Persevere�. So I am not going to give up on this engine. Even though it feels like it has given up on me.


John

John,


How far back is your plane's fuel-tank?

Some people incorrectly assume; that they can mount the tank at C/G and the engine will run... This would require a positive pressure, on-board fuel-pump.
The tank must be smack against the back-side of the firewall, for the engine to be able to run consistently both level and nose-up.


What did you change, if anything?

I am running a 13X6 Prop

The tank is in the same location as it always has been. Right behind the fire wall.

The replacement tank was a Sullivan Slant Flextank 16 oz

Well then, you do have a problem!

I wasn't trying to be pedantic, but it's good to know ahead that you went through the obvious basics of diagnosis. As I'm sure you know, on RCU many people post problems that turn out to be simple user error.

John,

Don't have the answer for you, sounds like between your own obvious common sense and a multitude of "possibilities" by other RCU folks the problem can't possibly continue to exist !!!!!
So, that being said, I have a good running Evo.61 on a Senior Telemaster and want to know what to do when it decides to give me fits. SO, DID YOU FIND THE PROBLEM?????????? Hope so.
Dan

May I make one more suggestion?

On my .36 the fiitings on the remote NVA started to leak after a while (3 years). The seals on these fittings are the fibre type and they seem to go bad after some time. This caused severe leaning and all sorts of troubles. Can you see bubbles in the fuel line from the RNVA to the carb? If so, that could be a possible problem. The fix is simple, just get replacemant gaskets and seals.

Hope this helps.

Anywhere you have fuel tubing you are going to have problems. I've had 3 or 4 of the lines from the RNV to the carb go bad on Evolutions. I just replace them now out of the box. Also, the vent line from the muffler takes hot gases. The inside of these get soft and collapse as soon as the engine heats up.

Speaking of fuel lines, I have seen some bizarre things happen with them in the past.

One person bought a few feet of silicone tubing and ran lengths of it to their engine in the airplane like you would expect. But the engine would not draw fuel or run. Eventually we found that the inside hole was missing on the piece inside the fuel tank Apparently it was a solid plug of tubing right there. You had to really look, it was hard to even see it. I remember someone else running into that problem here on the forum a while back too. So do try to see if the inner tube is clear in your tubing before you go to use it. You never know if some debris gets inside as well.

Another time was a piece of inside fuel tubing sloughed off the inner wall forming a one way valve. You could add fuel, but you couldn't get it back out. Then once there was a piece sloughing off the inner wall that plugged up the fuel inlet fitting on the engine.

Years ago at the hobby shop, I caught a kid poking pinholes in the roll of new fuel tubing with a needle. The owner was upset and the parent more or less took off with the bratty kid. I was hoping the parent would own up to it and buy the ruined roll of tubing but he took off before the owner could get him to pay for it. The owner took all of the rolls of fuel tubing off the wall as he didn't know how much damage the kid did or for how long.

So you never know, even that piece of new tubing you just bought could be bad.