Hi all,

I've been flying R/C off and on for about 8 years, but I can't claim to be an expert engine tuner.
Primarily because the engines I've owned have all run quite reliably with few issues.

Got a friend who's learning with a Nextar trainer with an O.S. .40 or .46 fx bolted to the front of it.

Here's the scenario:
Throttle back on downwind leg and then down to 10% power during final.
On the power-up to do a go-around, it occasionally quits when we hit the gas.
It doesn't do a higher rpm thing like it's out of fuel, it just... stops immediately.

If we don't let it idle too long, it transitions nicely, but if we idle back for 20 seconds or more, it flames out.

Always at the end of the runway.
I'm getting tired of dead-sticking my friend's trainer into the weeds.
So far no damage, but the math will catch up to us sooner or later.

I'm the friend Bosch232 is talking about. The engine is a OS 46 Fxi. Has about 20 flight total on it. I broke in the engine like the manual says.

Any suggestions would be helpful.

Has all the symptoms, due the pinch test it should die less than a 1/2 second and also the hold plane vertical and no change to too lean.
Counterclockwise 1/8 to 1/4 turn.. pinch test 1 second to increase RPM then die and vertical may show a little increase due to leaning. If too rich it will start to hesitate on power up 2 seconds on pitch before RPM increase and die.

Listen, you can have a perfectly tuned engine. This does not come from an ego thing but simply reading the fine print in the manuals which most ignore. All my engines run perfectly and some are even inverted and not one deadstcik due to tuning in years. it's a very simple process.

First, tune your engine as best as you think you can. But after you do this, how do you know what you did had any effect? By running a test on it, primarily these checks are to get the low end right. The high ends is generally a no brainer.

So you have the engine at an idle. Carefully remove the fuel line from the carb nipple or if you really can't, then pinch the line closed and wait for the engine to quit running. You need to carefully listen to the rpms. This is very important. If the rpms increase as the engine quits, your low end is to rich. If the rpms, just go down and quit, low end to lean. I usually try and get mine at a very slight increase.

With this. I rarely need to reset my low end in any given season and I have a perfectly tuned engine and they fly that way.


As for the high end, I really don't use the pinch/release method on th fuel line, mainly since most of my engines are cowled. But I help out others whos engines are exposed. If your high end is to lean and you do a pinch test, the engine wil probably quit when you pinch the line. I usually try and get it with a "no change" in rpms and it seems to be fine for them.

I feel I have the high end tuned pretty well. After flying last time w/ the deadsticks, I went home and reset the needle valve and readjusted it to slightly rich off max RPM at full throttle. Now it will cut out when you go from idle to full, unless you incr throttle very slowly.

Even though the glow plug looks OK, I will try a different on and I will try the pinch test at idle.

I have one question about doing the pinch test on the high end. I can only pinch the line between the needle valve and carb. If the needle valve adjusts high end, what will pinching the line between the needle valve and carb tell me????

From what I am reading, it almost sounds like your low speed idle is to rich. You may want to turn in the low speed adjustment a smidge and see if that helps. Good Luck, Dave

Mind you I'm a newbie at this, but I thought the same thing when I read the manual. I did lean it out some and then the dead sticks started. We thought we should back it off some and now it dies during ground check when transitioning from idle to full.

Maybe I over adjusted each time? If so, what is a good starting point to readjust from there.

My instructor helped me tune my engine. It was on the rich side. After a half dozen minor adjustments to lean it out on the low end, I was able to go from idle to full throttle with zero hesitation. Before the adjustments the engine would hesitate. No worries now.

somegeek

One thing that has not been mentioned but I think can help is to do your real fine tuning with less than 1/2 tank of fuel. Most of the time it makes no difference but on more than one occasion I have found it useful.
Fred

The adjustments on the idle needle are very slight, 1/8 of a turn at a time. Run your motor up, and blow out all of the excess fuel. Let it idle for 30 seconds (by the watch) and advance the throttle. If it sputters and hesitates, it is too rich. If it cuts out it is too lean. Adjust the screw in for rich and out for lean (remember 1/8 turn at a time) and repeat procedure. This can be very time consuming but you will eventually get your engine performing correctly.

If you do what I suggested, you will be able to tell immediately where you low end is at. If you get the low end right the first time, you rarely have to re adjust it for at least a couple months. I always tweak my high end before every flight.

Voborild, what size prop are you using?

The pinch test on the high end needle can sort of tell you if that needle is rich or lean. I try and get a no change in rpm but i usually don't use that method much

Hi Bosch232,
Did you change that glow plug after you broke that engine in?
That was a nice wing stress test you showed us!

Let me know if you go fly today.

the prop size is an 11x5. its the original one that came w/ the engine and the plane

I had a very similar problem with my OS 60 FP, where it would die on me if I throttled back for a landing; then if I tried to throttle up for a go-around it would quit on me.

Here is how I fixed this problem.
Perhaps it might work for you, the pinch test sounds good too.

1. Run at full throttle to clear out engine.
2. Idle engine for 30 seconds, then try to throttle up the engine. If it spits and sputters then the low end is too rich. If it just dies then the low end is too lean.
3. Make SMALL adjustments either way for your situation 1/8th turn

4. Idle engine for 45 seconds, then try to throttle up
5. Make any necessary adjustments as in step 3.

6. Idle engine for 1 minite.
7. Make any final adjustments so engine can idle for 1 minute, and then give a good smooth transition upon throttle up.

Good luck, and let us know how it works out for you.
Ryan

Ditto. This is basically the procedure I use, work very well. Would like to amplify. Be sure your high side is set before you mess with idle mixture. On the roll up to full then back (Step #1) don't bang the stick, roll it up over 1 second, hold for 3 seconds, then pull back to idle over 1 second. On #2, sometimes a lean engine will not instantly die, i.e. you get a quick partial spoolup of maybe 1000RPM then it dies. Be sure to perform the idle test with a warm engine. Cheers.

The 11x5 prop is fine. I use the same method as RhyanO to set up my engines, have been for years. It always works. Use a quality glow plug, like an OS# 8. 1/8th of a turn at a time, sometimes less is what is needed to get the low-end screw dialed in. Let us know how you make out voborild.

OK I have the bottom end dialed in pretty close. One question, what's the ideal setting for the bottom end? A little rich or right on? This may be basic, but the manual doesn't say so I'm wondering?

BTW check out my quickie test stand.

I think we did, can't quite remember.
He's got at least one new one in his box, because I owed him one and gave a new one back.

Winds are supposed to be under 10 mph tomorrow, lets go.
Sometime from Noon onward.

Hey, this is a question that's easily answered.

Try something.
And check to see if it helps or hurts.

Adjusting the idle is not really a mystery.
Start the engine and run it full throttle for a minute. Then do your idle test. Then shut 'er down. Turn the idle needle whichever way you think it needs it and run her again. Did it help or hurt? If you can't tell, repeat the same adjustment until you can tell. Then do what that tells you.

It's very complicated to write up all the ins and outs of idle-needle setting, but it's dead simple to do it. And it takes you almost no time to do it if you simply keep going in one direction until it's obvious if that's helping or hurting.

The only secret to it? Don't lose track of how much you've changed it. OK, there might be another. Don't stop changing until it's obvious the direction you're going is either right or wrong. Don't stop the first time you think it might have been better. Test the next step and see if it's still getting even better or even worse.

This is one deal that is better done than talked about. Just try something. You'll learn to do this far quicker trying stuff than reading stuff.

BTW, it takes what? 30 seconds? to shut down an engine, turn the idle needle 1/8 turn, and crank back up?

Yeah, there are a couple of important details.
Don't hamfist the idle needle. It's a fine adjustment device. 1/8 turn is good for each test. If the first test isn't obvious, do 1/8 and retest again until it is obvious.
And always open the throttle to do the low needle adjustment. Matter of fact, look into the venturi to see if you can see the needle while you're at it.

I've seen too rich idle needle settings kill the engine in the air. I've seen too lean idle needle settings kill the engine in the air. The symptoms overlap. But testing on the ground won't be fooled. And won't take any time at all.