I have an Evlolution .40NT that until recently has been a pretty good engine. One day while flying it went from flying great to dead stick in the middle of a flight. Checked everything and could not get it to start on multiple attemps and new glow plugs. I finally noticed that the set screw that holds the easy adjustment on the LS needle had fallen out allowing the needle to move freely. On all my other engines this would not be a problem as I could get a factory starting point from the manufacturer or at least get it close with the pinch test. Evolution however, doesnt have factory settings listed anywhere and the pinch test is a VERY rough estimate because this engine uses the LS needle to add fuel even when the throttle is at full. This causes the LS needle to be effective throughout the throttle range.

After basically guessing as a starting point and replacing the set screw I have the plane running but at full throttle I am still having surging issues as the LS needle is not doing its part in adding fuel.

What I need is either a picture (like the one I placed below) of someone elses LS needle to see if the back of the needle is flush, indented, or sticking out of the easy adjust block or someone who knows how many turns from,,,, something this should be. This should get me in the ball park. I have spent 3 full hours now on this basically chasing adjustments around instead of flying.
Any help would be greatly appreciated!!!

I went to the LHS to compare to another but the closest thing they have is a .61 and a 1.20.

I can get you a picture tonight.
But can't you adjust the low speed needle valve by listening to how the engine transitions from idle to full throttle. If you look in the manual it says that the pinch test is for the High speed needle, not the low speed.

The low speed needle is too rich if when transitioned from idle to full the engine stutters and wants to kill.
So start with it rich (turned out) and work your way in until it runs good again.
Every engine is going to be different so your engine might require a different number of turns of the needle than mine.

Also to prevent the screw from falling out again I suggest filing the metal so that the screw has a flat surface to make contact with and then use some loc-tite.

Josh,

The low speed needle position shown in your pic's is a good place to start, about flush with the barrel.

And Josh's recommendation as above should get you where you want to be.

The pinch test is most valuable at idle. The high speed mixture should be set by a tachometer reading, down 300 to 500 RPM down on the rich side from peak rpm. The sticky at the top of this form is very good for adjusting your engine.

FYI; there is no such thing as a factory setting for "proper" mixture strength. The factory does not know the atmospheric condition you will be running the engine in. Nor do they know the viscosity of the fuel or it's nitro and oil content. Factory settings is a marketing and sales tool to make one think the engine is easier to use. The fact is that it does not apply to the real world. In fact those needle limiters make thing even more difficult as the variables change and one needs to go outside the adjustment range of the the needle limiters. Let the engine tell you what the setting are not the marketing hype.

Friends don't let friends fly nickel,
Konrad

The needle is actually about 1/2 turn out or more from flush at the moment which is a HUGE difference for a LS needle if flush is where it is supposted to be. The pinch test is great for most engines, but as I stated before it doesnt quite do it for this engine because it is involved in Full throttle operation as well. If I get the pinch test down to around 4 seconds the motor will not advance past 1/4 throttle without dying no matter how slow you transition it. It is set to about 9 seconds right now and transitions to full throttle nicely but after about 6 consecutive seconds of full throttle operation the engine surges. If you increase the HS needle a little it wont ever hit full throttle.

Originally Posted by Konrad

FYI; there is no such thing as a factory setting for "proper" mixture strength. The factory does not know the atmospheric condition you will be running the engine in. Nor do they know the viscosity of the fuel or it's nitro and oil content. Factory settings is a marketing and sales tool to make one think the engine is easier to use.

This is true, but what I was actually referring to was the baseline that some manufacturers give you. It is almost always really rich, but it will run. OS often gives a __ turns out from full in position as a starting point for situations like this where I have no idea of where to start. In their defense, I dont think that there is any way to do this for the LS needle on the Evo as it has this collar and lock on it. Obviously though, when they set them up on their run stand, they must have a standard starting point that they dont feel the need to share in their manual.

I'm still having problems. I'm just not sure anymore. I have the lowspeed set so it idles nicely and transitions very well to full throttle. At full throttle it will hit high rpm for several seconds then will slowly drop rpm back to 4 cycle style operation, not adjusting anything at all it will then rev back up to full rpm after 10-20 seconds and start the entire process over again. It does this from 3 turns out on the HS all the way down to 1 turn out. I have now even mounted the HS back on the carb instead of the remote location. I'm flat out confused at this point. I will go back and try the LS at 3/4 turn out going in the rich direction and the HS at 2.5 going toward lean. The crazy thing is that it runs almost the same without dying at almost any needle setting with the same surge style full throttle.

I took the exhaust off after hearing of people having problems with the liner being mis-aligned. Everything that can be seen throught the exhaust port looks as it should. I looked at the OS 40FX manual and the baseline settings on that motor are 1 1/2 turns out for both HS and LS. Although not exactly the same I think that I may try that as a starting point???????? If I cant get it in another 30-40 mins of trying I will probably put a Pitts muffler that this thing originally ran fine on and try that. If that doesnt get it I am going to pull it out and have a look at the internals to make sure something isnt wrong unless anyone else has any better ideas. I have had two other guys that are very good tuners look at it. Both of them got it closer than I ever have but it still had the surging on the HS each time. Both times low speed adjustments were what got it closer.

You could try replacing all of the fuel line. Take the tank apart and cut new lines to length and put it back together. And also replace the line going from the HS needle to the carb. Make sure that the rubber stopper still looks good and is not leaking.
If you do replace the fuel lines I suggest that after you are done to fill the tank with fuel outside of the plane to be 100% sure it doesn't leak.
Also replacing the glow plug again might not be a bad idea. If you got some crap in the engine it could have damaged the glow plug making it run poorly.

Hi Funtana, and thanks for the tips. I decided the other day to run the motor on a completely different fuel tank that I rubber banded to outside of the fuselage just to check everything. It ran exactly the same. On the line from the HS needle to the carb, I went ahead and removed the remote mount and put the HS needle right on the carb now. Same running results. What rubber stopper were you talking about? That might be worth a look if it is something that I havent bypassed. The glow plug has been changed twice now, and one of the ones that I took out runs fine in another motor that I have.

The rubber stopper is the the black rubber piece that the fuel lines run through into the tank. It has the screw that holds it tight to the tank.

What is the remote mount? Could you have accidently changed something w/o knowing?

Maybe if you have a video camera and feel up to it you could shoot a video of the engine running???

Josh,

If you need a good starting point for the low speed needle: take the carb to idle, close the LSN, attach fuel tube to the carb inlet, blow in the fuel line and slowly open the LSN when you can first detect air movement stop. This should be a very good place to start from. Sorry just noticed you already solved that.

You need to check your carb for airleaks and or debris. Both can produce the symptoms you are listing. Take both needles out and fully clean the carb and re-install.

I might start with the blowing air through the line trick. I definately dont have the LS figured out yet. The Remote that I removed was the bracket that holds the HS needle. I pulled the needle out and moved it up to the carb. I did this hoping to cure the problem that I am having now. I just emailed Evolution to see if they could give me starting settings but I am thinking that there might be something else wrong now. Here is what has been swapped out with another part to test: Fuel tank, clunk line, clunk, vent line, rubber grommet, fuel lines (all of them), two different glow plugs (both the plugs removed work fine in other engines). I have also removed the exhaust, checked and reinstalled it. I will probably try another exhaust that I have. If that doesnt do it I will pull off the engine and check to see if I have a cracked piston or something. I will take a video before I remove it, that is a really good idea.

If case you have not seen this, it is a good resource for engine tuning.

http://www.rcgroups.com/forums/showthread.php?t=205602

Don't rule anything out, even small things like trying a different fuel can lend useful diagnostic information.