DLE 20 drops rpm after 10 sec idle
 

My DLE 20 seems to be developing more and more of a problem. When I have the engine at idle for about 10 seconds the rpm will drop suddenly to about 60% of what it was. I've never put at tachometer on it but it is a significant drop. So much so that if I set up the throttle trim for an appropriate idle for a flight, it will drop so low during landing that the engine will quit.The engine is mounted in a 1/4 scale cub with a 17/6 prop. The engine is about 6 years old and has about 50 flights on it. Other than this problem it runs great. Could this be ignition, possibly something to do with timing changing?
Thanks in advance
Roy

I think you might find that running it a little richer on the LS screw might make it a little less picky on it's idle speed settings. More forgiving all the way around actually (tuning as well as starting).

Yes, it's going to run a little rougher, but I'll take that over an unreliable idle any day.

Have you opened the spark plug gap to .025" or so yet? Sounds crazy, but that will help it burn that richer mixture much better...especially in mid range.

Plus one on the above advice. That is exactly what my 20's require.

I usually tell people that rich is reliable and lean is dead. Of course, the correct setting is somewhere between the extremes but as Hicks has said many times, a rich engine will at least keep running and you can adjust it from there to suit your preference.

I'm not sure I would describe idle as unreliable. Unfortunately what happens is very reliable. If I start out with a high enough trim setting it will always drop by about 1/3 of the previous RPM after about 10 seconds. It seams just like I brought the throttle down to a lower setting. It doesn't burble or stumble, or wander around, it just drops. Once it does this it stays at that RPM indefinitely. If I start with a low RPM setting it does the same thing but because I started out low, it will drop about 1/3 and now the idle is too low and sometimes the engine will quit. I don't notice it at about 20% throttle and above. Engine doesn't have any issues with throttle advance or coming off throttle, just at idle. Help me to understand how this is related to a lean low speed setting and not a timing advance issue. Thanks for your help guys.

Sounds like you may have one of the older DLE 20 engines that had the dreaded #4 ignition module. If you use a high idle setting as the engine's throttle is reduced to a certain speed, the module will dump all the ignition advance and the speed will just all of a sudden drop. This all happens at a speed I would call a "fast idle". Many people get around this by using a slightly rich LS needle setting but more users have found the only sure cure is to get rid of that ignition in favor of anything but the Rcexl #4. Maybe not your problem but you may want to look at your ignition module. If it has the #4 on it ..... I'll leave it to your own devices what to do with it. They only used that ignition module for a year or so then abandoned it in favor of one with a more normal advance curve.

That #4 module had a single "step" in the timing curve - and it was way to low in the rpm range to work right. Or maybe I should say work without issue. Some of us have the engine running pretty good with it. The step is at something like 2200rpm if I remember right. TR is correct stating many baled on that module in favor of one rated for 8.4v. If you see yours has that 8.4v rating, this step thing is not your issue. If you do have the older one - try going rich as stated earlier......

It's a cheap something to try that will only take you a minute.

If you have a 20 that's never burbling, I doubt it's tuned right. Great engine, but they run rich when they're right. ;<)

Last, it might help if you could pass on some rpm figures for what you're seeing. -Al

This #4 ignition module sounds like what I'm experiencing. The plane is in my storage unit at this time. This weekend I'll check. If the weather cooperates I'll get some RPM readings. Where do I look for the #4 mark? Where would I find the 8.4v mark. I'm almost sure I can't run higher than 4.8v with this module because I recall I couldn't run a 6v pack to power it. If I do decide to change it, do you guys have any recommendations as far as brands go? Thanks again for your help.

Here's a good one. Dan.

http://www.ch-ignitions.com/

Both the operating voltage and the model number will be on the ignition module wrapping sticker. The #4 mark was often just an ink stamping on the sticker though I have also seen it be a paper sticker.

Any later Rcexl module will work just fine as will the excellent CH ignition recommended by All Day Dan. Just be sure the one you get has the right plug end to fit your CN-6 plug. You can buy Rcexl ignitions from most any source that sells engines. Valley View RC comes to mind as does Tower Hobbies, etc. just to mention a couple. The Rcexl is probably the most popular ignition in use these days,

The RCxp line of ignitions is also a good choice and they are available from RC Extreme Power at this web site. With the correct connectors, all the ignitions mentioned here are directly interchangeable.

http://www.rcextremepower.net/

First, unless you demand the latest and greatest just because you know it exists, I wouldn't be too quick to abandon a #4 module. Mine is still in use, and still running great on what many would consider a high time engine. As you build time with this engine, you'll likely be running it a little on the fat side anyway. Most everyone I know does, myself included. It just makes for a great handling little engine that makes all the power you could expect from something in this size and weight range. An over achiever if you will. All of which is the long way around of saying that if you can stand keeping the engine a little fat, you'll probably get along with the dreaded #4 just fine - knowing what to expect from it. Just keep that idle away from that 2200 "step".

If you decide to buy a module I would recommend the RCXP as it's the latest and greatest, with the latest thinking incorporated into it's internals. It's been blessed by those that have forgotten more than I'll ever know on the topic. It's lighter, a little smaller, and priced right from Extreme (less than many get for Rcexl modules). -Al

Hicks, once again I agree with you regarding the #4 ignition ..... if the user understands what is going on and can live with it. One good friend of mine has an older DLE20 on a SIG CUB. This elderly man is very intelligent and a retired aerospace engineer but no matter how I tried to explain the #4 ignition to him ..... I just don't think he ever fully understood what I was trying to explain. The engine is good as long as someone else sets the needles and throttle curve. And (usually during landing) as long as the throttle is either all the way down to idle or just above the step point it is OK. But touch that throttle and the RPM's jump up in a way that startles him every time.

I'm the kind of guy who couldn't tolerate that sort of thing and would replace that ignition in a heartbeat! But that's just me!

As somebody that appreciates a greased in landing as well, and in full knowledge of the fact they often need just the smallest bump of throttle deep in the flair to do that - I can say I haven't had the issue there.

BUT!
As a "wannabee" 3D flier who LOVES play in high alpha to the 'n' th degree, I do run into that step, and it's a pain in the butt. I've survived to date by moving that module to a plane in the hangar where that part of the low end control is not so important. Actually, I wish this #4 would die, finally giving me the excuse necessary to try one of the RCXP modules.... -Al

I like how the Rcxp module makes a couple of my engines run. It has a bit more aggressive advance curve than the Rcexl units so acceleration is a bit more crisp if that makes any sense. The advance drops out nicely when throttled down so there are none of the Rcexl #4 type of issues. The spark is also noticeably brighter and louder when watching a plug inserted in the cap. As a result, starting seems a bit easier and I believe the engines tolerate a bit wider fuel / air mixture at all needle settings. Disclaimer here though ...... I have no real complaints about Rcexl ignitions unless they happen to be paired with one of the problem sensors that pop up from time to time.