Balin

I've got a Magic, OS 46fx, stock muffler, 11.5x4 prop. High end needle is about 400 off peak (set at about 12000). Low end is as good as I can get it, ie transition is fair, though lags a bit when I punch it. I'm not safisfied with it but can't seem to get it any better.

This is my first glow engine, A lot of the "tests" for idle mixture seem too ambiguous for me to distinguish between. Ie. "If it stumbles and coughs and dies it is too rich. If it chokes and dies it is too lean." Yeh, right. Like I can tell the difference between stumbling and choking.

Anyway. I do a flat spin, engine idling. When I hit the throttle it dies. I can keep it alive-ususally - with a more steady throttle up. Am I asking to much? It will also die after a outside loop at idle followed by full throttle.

Am I too aggressive with the throttle or should it transition. Is my tuning off. Or what?

Possibly related: the only way I can get fuel into the carb on first start of the day is by choking the carb with thumb and running the starter on it for 20 or more revs. It's fine the rest of the day.

Thanks, Balin

C_Watkins

My Feedback: (10)

Sounds like the low end is lean.
I think a lot the Magics have a bit of a "first start" problem, though they aren't that bad.
The "very tall" mains place the tank outlet FAR below the carb. Mine always gets
fuel by the second flip though, if I have a finger over the carb or muffler outlet.

Which again leads me to believe your low end is a tad bit lean.
Open the low end adjustment 1/8-1/4 and re-tweak the high end when you get
it warmed up, just like you have it now. (300-400 off peak) Then fly it again.

Just remember where it was, to put it back if you don't like it any better that way.


Having a lean low end, combined with anything that would throw fuel "away" from
the direction of the carb, makes it tougher to draw fuel. Sometimes a fatter
low end will help. You might also check that your muffler seals well, and that
you have no leaks or kinks in the pressure line to the tank. (or leaky tank?)
Maybe even a one way checkvalve in the pressure line might help.
But do try the simple stuff first

JoeyCoates

I agree, sounds lean. I have a magic with a tt36 pro and it was doing the EXACT same thing yesterday. Richened it up some and it was fine. I can do a flat spin now and with proper application of throttle aileron and elevator I can actually get it to gain altitude. Very cool.

bentgear

Balin, will it run the tank dry if you don't try to spin or loop it? If not klunk may have stuck forward in the tank or even come off. Let us know what you find.
Ed M.

Balin

Thanks for the tips. I'm going to start it up later and adjust the low end, although I won't be able to flight test it. It's very possible the low end is lean as I set it yesterday for a fresh start at the OS manual setting of 1 1/2 open. I ended up with it a just a bit over 1 turn open. Like I said, trying to decide whether it is rich or lean has me a bit boggled.

I can run the tank all the way down if I don't kill the engine like I described. I tested the tank endlessly for leaks, but yesterday I noticed some tiny bubbles in the line. I have to look at that more closely today. Is there any amount of bubbles that is OK? I've only noticed as I was starting, and after that it was in the air. Well I'll find out that too.

I've got the muffler to engine surface sealed with RTV silicone and all the tubing (except after the needle valve) is clamped with plastic ties.

Thanks, Balin

Balin

Ran it up a while today. It has a tiny stream of little bubbles at full throttle only. Reading here I learned the fuel tubing on the needle valve trick and did that. Made no difference. I just can hardly see the tubing that comes into the needle valve so I can't see any bubbles there. Not ready to redo the whole tank yet. But there are bubbles at the top of the fuel in the tank from vibration. I don't see how they get into the fuel line though?? Do they?

Seems my best results at this point are programming in a 800 rpm idle up condition and running with that and just using the in:dle down for landing.

Balin

goony

The way I have been shown to sort the bottom end is to get it running at a fast tickover say about 3500rpm with about half a tank of fuel then hold the model nose up and with a long screwdriver adjust the bottom end until u get max revs then adjust the main needle whilst keeping the nose upwards doing it with half a tank means that when u fill it up it should run slightly rich and when nearly empty it shouldnt go to lean

regards goony

Balin

goony,

Thanks, I'll try your method to "double check" what I got today.

I reset the low end needle to 1.5 turns out (as per manual).

Started it up, set the high end. No problem. Got the idle to about 3200 and waited. The rpm slowly sank to about 2500, sonding a bit worse as it went. Then I gave it full throttle and it stumbled, shot drops of fuel (and smoke) out the exhaust. I figure the slowly diminishing rpm is the engine loading up and running richer. Any confirmation on that?

Screwed the idle needle 1/8 turn leaner and repeated with about the same results but a little improved transition.

When I got to where the idle screw was 1 full turn out I noticed (pretty sure on this) that the drop in rpm as I waited was less than before and the transition only had a bit of stumble.

One more 1/8 turn in. Started it up. Tthe idle sounded sooo smooth. The sag was just about nothing and the transition was perfect. I hope I am right, because I finally felt like I HEARD the engine. I richened it back out to 1 full turn for tomorrow's test flight.

Ignoring the high end bubbles for now. Lots of bubbles in the tank, on the surface, but it's not foam. Just big vibration air bubbles that go away as soon as the throttle is backed off. Could be getting in the line though.?

Balin

edberry22

I dont know if this will help but it was offered to me as advice when I had the same problem.
Add an inline fuel filter, it did seem to lower the amount of bubbles in my fuel line but never really got rid of them. Another person said a few drops of armor all in the fuel acts like an anitfoam agent......have not tried this myself but am passing it along.

I had not flown R/C in a very long time and having just returned, I noticed some changes, I notice that the fuel line wants to "sqeeze" itself back off almost any nipples its attached to(after its wet with fuel)are the fuel fittings being made slightly smaller then 15 years ago, or the fuel line, or maybe the materials used in either are somehow effecting the fit once exposed to glow fuel? I have never had this much trouble with fuel line in my life before, then again, twist ties never came with fuel accessories before either.........never needed them.....you attached the fuel line and it stayed put until you removed it to refuel or whatever........hmmmmmmm.........makes ya think a moment doesnt it? I am betting that the air in the fuelline at least on my plane is a product of this and is being sucked in thru a fitting, somewhere, somehow. My tank compartment is foamed, as per instructions, all my planes are, but its the one OS engine that gives me the air/fuel line fits.
Maybe I will try a different brand of fuel line on my next build.

Matt Kirsch

My Feedback: (21)

Yes, slowly diminishing RPM is called "loading up" as in the engine is pulling in more fuel than it's burning, and the crankcase is loading up with fuel.

Adjusting the low end is hardly ambiguous. You described both "stumbling" and "coughing" in this thread to perfection, in their appropriate situations.

The test: Allow the engine to idle for a solid 10-count, then quickly push the throttle to full.

What to look for:
1. Gradual slowing of the engine during the 10 count. This indicates the engine is loading up, that the idle mixture is too rich.
2. A noticeable drop in RPM when you remove the glow starter. This also indicates the idle mixture is too rich.
3. Stumbling, excessive smoking, spitting raw fuel, or a combination of the three. This indicates the idle mixture is too rich as well. Unless the engine is REALLY rich on the low end, it will not quit running.
4. A cough or sag, followed by the engine quitting. Think of a cheesy movie death scene to envision a cough. The dying character emits a single cough before giving up the ghost. This indicates the idle mixture is too lean.

Balin

Mkirsch,

Thanks for the feedback. I think I'm starting to get a handle on this. The 2 hours I spent out back yesterday just experimenting - lots of vrooom, vrooming, really started to educate my ear. The neighbors have been a bit unfriendly today though. Oh well, in the name of modelling...

I think the "cheesy movie death scene" cough should be entered into all future engine manuals. Perfect

Balin

Graeme Marion

Try squeezing the fuel line briefly with your fingers while the engine is idleing.

If this makes the engine speed up then the idle needle is set too rich.

If squeezing the fuel line with your fingers makes the engine quit without speeding up then the idle is set too lean.

Just my five cents worth.

mymagic3d

mine was doing the same thing, but I think I fixed it by richening the bottom end still have to try it though

Spaceclam

I am a proud owner of a 46 fx. i don't know what you've done, but mone has no hesitation when i full throttle it, and it has never once quit in the air. i have done torque rolls, and everything you can do on a trainer. i have never had any trouble with it. i run a 10x7, it seems to be an ideal prop. here's what i did to get the low end right. keep in mind i am running 15% so it has a bit more punch. the factory setting is for 10. you will have to lean it out a bit to get it to spool up seamlessly, but if you lean it out it will hesitate. i assume from the other posts that you have already richened it out. first peak it, and then turn it back to about 500 below. i don't recomend adjusting the low end while it is running. floor it really quickly and see what it does. if it is not perfect, it will hesitate nomatter whether lean or rich. but try richening it out first instead of leaning because too rich is alright, but lean is dangerous and possibly harmful to your engine. if it gets worse when you richen it, bring it back to it's origional position, and turn it the other way about 1/16 turn. it is very sensitive. keep it up until the spool up is seamless.