Originally Posted by Geetarjoe

I had the same issue with my DLE 20. It also had the aforementioned "miss" or burble about 1/2 to 2/3 up in the throttle range. running the engine and adjusting as it breaks in was the biggest factor in curing these issues. ive got about 3 gallons through it. the miss is almost completely gone now, and I can get a very low but reliable idle. I found also that once the engine is broken in you can get it to idle at a surprisingly low RPM. once you get it to idle down to ~1600 youre far enough away from that "bump" in the timing curve that it doesnt seem to be an issue. it also does like to be a little rich on the LS needle. that helps the engine slow down a bit when you close the throttle.

I agree... the engine has to get broke in. Ive got about 5 gal thru my DLE 20 and the missing issue is gone, the idle drop is gone, transition is smooth with no "burbles", its now got tremendous power and will start when warm with a slight "flip".

Let it run rich for a while (couple of gallons more) until the idle gets noticably rough. I was having trouble with the engine loading at idle when it finally got broke in. It will actually tell you when its time to start leaning up. Also, very, very slight adjustments when leaning... this engine is VERY picky to needle movements.

Be patient. it will come around.

Here's a throttle geometry diagram posted by jedijody.



I found the diagram took some time to understand and I had some questions I needed to confirm with Jody. Here are the conclusions:

1. The throttle position is 53º when fully closed
2. The centre of the throttle arm link is 0.8938" from the centre of the throttle shaft
3. The throttle shaft rotates through a 65º arc
4. The throttle position is 118º when fully open
5. The servo is at throttle off in the first picture
6. The servo arm is placed on the servo pointing directly towards the center of the throttle shaft
7. The centre of the servo arm link is 0.6700" from the centre of the servo shaft
8. The servo rotates through a 120º arc


Given these specifications the throttle shaft will rotate...


0º with 0º of servo rotation
1º with 20º of servo rotation
9º with 40º of servo rotation
21º with 60º of servo rotation
35º with 80º of servo rotation
50º with 100º of servo rotation
65º with 120º of servo rotation


This is a guideline. Some degree of radio programming will almost certainly be required.

OK, I had to ponder that a while grosbeak, but it now makes perfect sense!

I couldn't see, at first, what difference it would make where the throttle servo arm was positioned as long as it fully opened and closed the throttle with the required arc.

BUT considering the diagram, or more specifically the geometry, with the throttle arm pointing laterally at the throttle arm slight variations in throttle servo arm movement (arc) @ idle would hardly translate to ANY movement of the throttle arm ergo = a more 'stable' throttle butterfly @ the fully closed (idle) position. Which is exactly what Kerwin posted;

Originally Posted by kerwin50

Your stick to servo control horn ratio movement should not be as much on the lower position as the upper half.

COOL!

It's the same with 180 degree mechanical retract servos if you've ever screwed with them; The majority of gear movement happens between 20 degrees and 160 degrees of servo arc. The first and last 20 degrees of servo travel (arc) actuate the retract mechanism only very slightly. It's really swinging @ 90 degrees...................

OK, whether or not this cures my idle, this is some good chit!!

Well, if I ever do sort this out 'Grosbeak' you and your tutorials will have been a HUGE part of it. I'll owe you a beer(s) !!

After reading further in this thread, i think you need to go back to the basics....

There are only 2 reasons a GAS engine will either run or not run.... FUEL and SPARK. thats it, nothing else.

Most of the time, we are our own worst enemy when it comes to troubleshooting. we either blow it out of porportion (which is I believe what we have here) or we just simply dont know. We have gone from simple carb settings in this thread to throttle curves (?) Really?

Have someone knowledgeable set the carb and check the ignition. Start from scratch. Eliminate the obvious. I went through almost the same issue with a 20 myself and found it was a plug wire. But, I spent $100 bucks on parts i didnt need (Carb, plugs, etc.) because i just didnt know.

How do i know that this will work? Ive banged my head just as hard trying to figure the same stuff out!

Originally Posted by deason

Have someone knowledgeable set the carb and check the ignition.

Took a complete ignition from another DLE that ran flawlessly and swapped it out, no joy, and had everyone short of 'Jedijody' and Ralph Cunningham himself take a turn setting the needles, including a former NASA (I live space coast FLA) propulsion tech that worked on the Saturn V. He was, is, a rocket scientist. His experience in radio control dates back into the forties when radio control was 'top secret'. He was on task when Joe Kennedy Jr. lost his life. His take? 'It shouldn't be doing that'. I know at least that much. So much for a career of dedication to the 'technical'.

But, you are correct. If and when I figure it out? It will have been something simple.

And I would take the simple advice of; "Stop worrying about it and fly the model. It needs X gallons of fuel run through it before it breaks in". Although that's possible it's not practical. The surging makes final approach an 'almost' mishap every time. The only way to settle the model down is to kill the ignition on short final. A model I have no opportunity for go-around? Is called a 'glider'. I have no use for a P-47 'glider'.

The only 'obvious' solution to all this is an opportunity that dissolved back when I first took tool to engine; return it for replacement or refund through 'warranty'.

Now? It's just s learning experience. I'll (we'll) figure it out!

Originally Posted by FoamieAirfarce

Well, if I ever do sort this out 'Grosbeak' you and your tutorials will have been a HUGE part of it. I'll owe you a beer(s) !!

I'm sorry they haven't helped so far. But when (not if, but when) you do get this sorted, skip the beer(s) and post a new video of your engine idling smoothly instead.

Great attitude, awesome plan! It WILL be something stupid. Maybe it's time to pull the engine from the airframe and put it in a test stand?

You replaced the ignition, what about the battery? Have you tried a different one? Just guessin....

That diagram showing the extreme differential geometry is one I've promoted the heck out of as well. To expand on it just a little, it should be noted that if you start with the servo arm as it's shown in the first diagram (0) you'll have very little, if any, control of your idle speed? If you'll start with the arm closer to where it's at in the second diagram (20) you'll have all the differential needed to accomplish what you're trying to do - and maintain your ability to adjust your idle speed, and/or kill the engine with the throttle. The diagram isn't really wrong, it's just illustrating a point - extreme differential?

K.I.S.S.

Originally Posted by vmceachern

K.I.S.S.

LOL....Yep.

The simplest thing to do if she's still under warranty is to send it back.
Till the warranty runs out, its their problem, not yours...

And BTW, just because someone is a rocket scientist doesn't mean they are a small engines guru. Sorry, I just couldn't resist that lol.

Originally Posted by AHicks

You replaced the ignition, what about the battery? Have you tried a different one? Just guessin....

That's a point I haven't addressed as the engine runs EXTREMELY well every where up and down the throttle curve, aside, of course 'idle'. But that suggestion lends me to believe perhaps the remote ignition kill system may be suspect? Currently the model is run entirely on one A123 6.6V, through a HD Super Switch, and then a 'Spark Switch' ignition kill off the Rx that doubles as a 5.9V regulator to the ignition. I will run the engine with a straight battery to the ignition and see what happens.

I also agree that perhaps a 0º with 0º servo arm to throttle body @ idle would be too 'flat' and counter productive toward 'trim/sub-trim' especially to the low/cut off side. I'll set up the geometry as you suggest; something more along the value(s) of the second diagram.

Thanks for the input and support!

Originally Posted by deason

LOL....Yep.

The simplest thing to do if she's still under warranty is to send it back.
Till the warranty runs out, its their problem, not yours...

Yeah, there have been many in front of me that have returned both the 30cc as well as the 20cc DLE's back and received good satisfaction. These lower displacement DLE's seem to be hit or miss. Some are amazing out of the box and some are duds. China is certainly NOT synonymous with 'quality control'.

I kind of forced my hand with this model tho'. The install is in a scale cowl with very little air egress toward pressure equilization;



The engine has enough air on the cylinder to run cool, but there was a lot of pressure build up inside the closed cowl that caused a rich mixture condition and horrible *missing* in fast straight and level flight. That was install specific and not necessarily the fault of engine design. Returning the engine would have yielded nothing. I did the 'pressure equalization mod as per 'grosbeak' 's tutorial;



and it worked absolutely perfectly. But I knew full well I instantly voided my warranty at that point.

BTW the loping has been prevalent since before I did the pressure mod so there is no correlation there.

Originally Posted by deason

And BTW, just because someone is a rocket scientist doesn't mean they are a small engines guru. Sorry, I just couldn't resist that lol.

Ha! Too true!

I think I may see your problem..... that hole you have cut in the firewall around the carb... looks a little tight (?)

What you may have is a fuel problem, which from the surging sounds like the carb is not getting a suffecient supply of fresh air. That would also explain the "miss". there is not enough air to mix with the fuel thus making the engine run rich, even though its not SET rich. And since the cowl is so tight, air may not be able to make it in fast enough to "feed" the carb with enough air.

Engines HAVE to breath. For both cooling and proper air / fuel mixtures. I would take the engine off as is and run on a test stand. See if there is a difference in the sound of the engine both at idle and through its rpm range. If it changes, have someone WHO KNOWS ABOUT GAS AIRPLANE ENGINES to set the carb for the test stand. Put the engine back on and open it up... you may have to alter your cowling length to get the carb out of the firewall enough to breath. Or, a simple velocity stack may do the trick.

Guys???

This has got me curious. I'm anixouis to see if the geometery does the trick.
I have both a DLE 30 and a 20.
Both run like swiss watches.
My 30 started giving me a miss when my Nimh went bad. But changing it to a regulator and LiFe battery fixed that.
My 20 has the new ign and gone now is that timing jump.
She was very easy to tune.

Originally Posted by deason

I think I may see your problem..... that hole you have cut in the firewall around the carb... looks a little tight (?)

What you may have is a fuel problem, which from the surging sounds like the carb is not getting a suffecient supply of fresh air. That would also explain the "miss". there is not enough air to mix with the fuel thus making the engine run rich, even though its not SET rich. And since the cowl is so tight, air may not be able to make it in fast enough to "feed" the carb with enough air.

Engines HAVE to breath. For both cooling and proper air / fuel mixtures. I would take the engine off as is and run on a test stand. See if there is a difference in the sound of the engine both at idle and through its rpm range. If it changes, have someone WHO KNOWS ABOUT GAS AIRPLANE ENGINES to set the carb for the test stand. Put the engine back on and open it up... you may have to alter your cowling length to get the carb out of the firewall enough to breath. Or, a simple velocity stack may do the trick.

Guys???

Thanks deason, airflow to carb certainly is important. Your points well taken. You are the second poster who recommends putting the engine on a test stand. My only hesitation? I have to build one But, I really should have one.

Today I bought a replacement throttle servo to replace the JR 821 I am currently using. This is from the Horizon Hobby website;

"The JR821 servo is a powerful, accurate sport digital servo recommended for RC airplane applications up to 1.20-size. For helicopters, the DS821 operates best with 30-size glow models, and up to 50-size electric. Loads and vibration in larger models may cause premature failure of the servo resulting in damage or injury to property and persons"

Hmmmmmmmmm....................

The replacement is a Hitec HS-645MG. An old standby work horse high torque analog servo. I'll set it up with the proper geometry. And I'm also going to seal the rear case with a gasket cut from a Felpro rubber-fiber stock gasket sheet. I read elsewhere on the site where a modeller was having trouble with idle on a DLE 30, not surging per se` but troublesome, and adding the gasket worked. Apparently the machining of the rear case to front section was errant and the motor was sucking air into the crank case.

If these steps don't work I'll remove the engine form the air frame and run it on a stand. In any event I'll video the next trial run-up. Regardless of what I have done to this engine it behaves exactly the same; a good reasonable choke to *pop*, four more flips and it fires, runs up well, idles good until it gets up to operating temp and then it lopes..................

Thanks again for all the helpful comments

You've got a great attitude about this even if it is a frustrating problem. You will sort it out!

Do your servo and geometery 1st. I seriously doubt is you have a leak in your cases.
I do not use test stands much on gasoline engines because of the vibration. Your plane with the wings on is the best test stand you can have.
minute changes on the throttle control arms will give that type of surging. it only takes 1 to 2 mm of slop and she will give you the very same issues that you have.
Also disconnecting your throttle spring can cause this.