ENGINE OUT

I wanted to share my experience last week on a trip in my 6A in the hopes others will be better prepared if it should happen to them. Our 6A has an ECI IO-360 Titan engine with 115.5 hours on it. When descending into the pattern for a fuel stop the engine became very rough when RPM's were reduced to 1450. Anything below that was was impossible to hold. Playing with the mixture helped if it was leaned- richening caused more problems. Adding more RPM's helped to a degree. Now I am thinking of water (both tanks were checked during pre-flight and were fine) in the fuel or maybe a fouled plug but all the CHT/ECT's looked on the money. In fact all the gauges were reporting normal. I landed a bit fast, took on fuel, did the run-up which was fine and headed to my home airport at KLZU which was only 12 miles away. Enroute more problems with the engine- this time rougher. Asked for a straight in approach with no delay which was approved. Engine quit on the glide slope with 4 lights left in front of me. Landing was fine.

Problem- the spring on the idle mixture had broken off in flight and mixture screw vibrated to full rich position.

Lessons learned-
1. Next time an in-flight problem occurs a mechanic looks at it before we fly again. Abnormal operation is caused by something- we will address it and get it fixed.
2. We are going to remove the cowling every 3 months for an inspection.
3. Leaning would have made the engine run alot better- I should have tried it and noticed the improvement instead of using the usual settings.

Pete Joslin
RV-6A
IO-360 ECI Titan Engine
115.5 hours

I had the exact same thing happen

only Superior XP-360 with a Precision Airmotive MA4-5 carb except my mixture screw backed out completely and fell off in flight. You would never believe it could happen! I called Precision Airmotive, they promptly sent me a new screw and spring and I reinstalled. I put some torque seal on it this time so I can verify on preflight. Apparently, this has happened to others...

See this thread... mixture screw problem

another system that's not foolproof...

Glad to hear things worked out safely!


I hope we don't have to add carburetors to the list with electronic ignitions and fuel injection. Now if a magneto causes an engine stoppage, I think we're sunk...we'll have to buy glider kits.

Just kiddin! Glad you resolved it!

This tends to support my personal theory that most people have their mixture setting too rich. I hadn't thought that one of the consequences is that the mixture screw may have insufficient spring pressure and fall out...

Martin on Oz

In phase 1 at 13 hours TT, I had 2 consecutive engine out scenarios while in the pattern.
While still learning how to slow this puppy down in the pattern, I pulled the throttle back to idle while abeam the numbers. The engine sputtered & ran rough on turning to base. The prop stopped windmilling on short final. I didn't really have the time to troubleshoot in flight as I was on short final and had the runway made. I had originally thought the fuel moved away from the pickup tube, had 5 gals in that tank. I rolled off the runway & restarted with no problems.
I repeated the exercise and had the same results.
After consulting with Superior, we agreed we had an over rich condition.
They said they intentionally send out their engine set on the rich side due to the ability to use auto fuel. I adjusted the mixture slightly and have never experienced the problem again. I also do a much better job managing the speed into the pattern with my FP prop.

Happened to me too!

During my phase I, one day I tried to set my idle mixture so at mixture cut-off the engine will pick-up 50 rpm. Even after turning the needle screw very loose I never saw the 50 rpm raise. After the adjustment I went up for one circle in the pattern. Upon touching down, my engine quite on the runway. I re-started it and taxied the airplane back to my hangar at high rpm (low rpm would run very rough). Only then, I found that the idle mixture screw were gone. When I ordered the replacement, I was told that it happened to quite a few people. It only cost me $70 including shipping and no scare (the needle must fell upon touch down). But, it could be much worse. I also wonder why the screw is only held by the spring tension.

Be careful, don't turn that screw too loose. Local AP told me few engines he serviced ever made a few rpm raise at idle cut-off. It sure not on my engine. Another lessen learned is always test flight in the pattern after making any changes to your airplane.

Ted
http://tc1234c.googlepages.com/
RV-9A, Lycoming (ECI) O320-D2A, 160 hp, Carb, Dual Mag, Sensenich FP
GRT dual DU H1, TT DigiFlight II VSGV, 130 Hobbs 3/25/2007

If an engine is not responding with an rpm increase when the idle cut off is engaged, there is a problem. It should raise 25-50 rpm. If it is less, that usually means too lean. More means too rich. All the carby planes I ever flew exhibited this.

The spring tension is what keeps it in place, so if you are running way rich the tension will be less and the screw prone to backing out. Always adjust the carb when the engine is fully warmed up, like after a flight. Just warming on the ground does not always get the engine warmed up enough or it could be warm, but plugs slightly fouled from ground running in a rich condition. The engine might not respond properly.

Follow the engine MFG instructions for adjusting the carb mixture.

Roberta

Mixture screw adj.

Hi Roberta,

I believe that the 50 rpm increase when pulling the mixture is only a guide. My Lycoming doesn't do it, and I think that chasing this setting may cause more serious problems, such as losing the screw altogether and having the engine run rough or stop.
I have discussed this with Mahlon at Mattituck (on the Lycoming List) and he didn't seem to think there is a problem in not getting that 50 rpm increase, as long as the engine ran smoothly and didn't stumble or stop when pulling back to idle on final, which is what the whole purpose of the exercise is about. I guess every engine is a little bit different, so whatever works individually is fine.
Cheers

Martin

Hi Harvey,

Lycoming specifically states you should make necessary adjustments until you achieve the momentary 50 rpm rise during the idle cut off check. Meaning as you slowly pull in the cut off, you should see a brief rise in rpm (25-50) just before the engine cuts out. This should be done at proper idle speeds and temperatures and you may need to readjust the idle speed as you zero in your mixture. I'm sorry but I totally disagree that this is not an issue. I have been around engines and airplanes for 40 years as my livelyhood. I don't want to see someone needlessly have to land engine out because of a mall adjusted carb. It's really easy to do properly. This is not a some do and some don't thing. They all should. I believe my mixture screw is only out less than 2 turns from bottomed out in.

Here is a link to Marvel outlining the importance or adjusting the carb.

http://www.kellyaerospace.com/articles/Accessory_AMT.pdf

Don't mean to flame anyone.

Roberta

Roberta,

Thank you for the AMT article. I, for one, have no engine experience before building my airplane. Any advise is welcomed. When I tried to adjust idle mixture I did follow the instruction from my Engine Operator's Manual yet did not see any noticeable rise. Fortunately, so far the engine runs well at idle (I have a 9A and usually pull throttle idle before turning base). The AMT article points out something not in the Operator's Manual:

"Any fuel-borne contamination or corrosion latently within the carburetor can migrate to these idle passages and create a lean condition at low power settings. If the contamination is significant, it will not allow for proper fuel/ air ratios at idle. At sea-level, mixture rise as indicated on the tach should be approximately 25 to 50 rpm. At higher field elevations of 5000-ft. or more, the mixture rise will be more in the neighborhood of 75 to 100 rpm. An idle adjustment screw that requires more than four turns out to achieve a proper mixture rise at ICO is a good indication of contamination in the idle circuit."

Could the above the reason that some engine does not have the 50 rpm rise at ICO? Or, it is just a reason. What are other ill effect of not achieving the 25 to 50 rpm rise at ICO? Any advise on how I might get this problem solved?


Ted

Idle RPM

robertahegy said:

Hi Harvey,

Lycoming specifically states you should make necessary adjustments until you achieve the momentary 50 rpm rise during the idle cut off check. Meaning as you slowly pull in the cut off, you should see a brief rise in rpm (25-50) just before the engine cuts out. This should be done at proper idle speeds and temperatures and you may need to readjust the idle speed as you zero in your mixture. I'm sorry but I totally disagree that this is not an issue. I have been around engines and airplanes for 40 years as my livelyhood. I don't want to see someone needlessly have to land engine out because of a mall adjusted carb. It's really easy to do properly. This is not a some do and some don't thing. They all should. I believe my mixture screw is only out less than 2 turns from bottomed out in.

Here is a link to Marvel outlining the importance or adjusting the carb.

http://www.kellyaerospace.com/articles/Accessory_AMT.pdf

Don't mean to flame anyone.

Roberta

Click to expand...

Roberta... Lycoming also says (in the Operator's Manual) that the idle speed should be adjusted for altitude, but doesn't give any numbers. This has to be set before any ICO checks are done.

I found a link that quoted 10 to 15 rpm less per 1000 ft altitude, but could not find a Lycoming spec.

Do you have a link to numbers for this altitude adjustment?
I know it doesn't make a lot of difference in WI, but we are at 4000 to 5500 DA most of the year...

gil in Tucson

Just curious, are you guys looking at a digital tack or a mechanical tack.

Just when I think I have my plane dialed in, running great, you guys (and gals) bring up something else for me to worry about. lol

Okay, so on shut down, I lean the engine out, it just quits, it does not raise RPM. Last year I noticed at high altitude landings (I'm at 1,500MSL, and I was in CO at 5,500 MSL) I noticed the engine missed and was tough to start until I leaned it out.

Should I be concerned about running too rich? Am I set too rich? Plugs look great.

Digital

casper said:

Just curious, are you guys looking at a digital tack or a mechanical tack.

Click to expand...

Digital (Horizon) ... though it's easy to calibrate a mechanical one with a model airplane hand held tach...
My old mechanical one read 100 to 150 rpm low... which I believe is typical...

gil in Tucson

You should actually be able to sense the momentary rise in RPM just by listening during shut down. I have an EI digital tach so I see the rise quite easily.

Higher altitudes may actually see higher rises in RPM when properly adjusted, according to the article I linked.

You need to lean more at higher altitudes. When I land at airports higher than 4000 msl, I leave the engine slightly lean on landing. Taking off you also need to lean a bit. I'll pull the mixture out during runup to smooth things out prior to TO, especially places like Aspen or Leadville. The leaning runup is done at higher than normal rpms to make sure you don't lean too much and still have proper TO power.

Causes for carbs not responding properly could be air (vacuum) leaks in the intake system, improper float level, dirt or varnish clogging passages in the idle circuit, the cutoff circuit clogged or leaking and/or engine not warm enough

I set my engine idle at 650 rpm during my initial setup. I made sure the engine was warmed to operating temperature. I initially set the mixture while the engine was running to get the fastest idle speed while adjusting only the mixture screw. I reset the idle to 650 rpm, cleared the engine by running up to 2000 rpm, returned to idle, and pulled back the cutoff, watching the engine speed on the tach. You must pull back slowly as you watch the speed either increase or just drop off. As you get near the end of the travel you should see some change. A too rich condition will show a large increase in rpm. Too lean will show little or no gain.

It's important that the mixture screw not be turned out too far in doing this procedure. This screw is normally not turned out more than 2-3 turns. That spring needs to be compressed to hold the screw in. Making adjustments is done in small increments, and clearing the engine between adjustments.

Hope this helps. Do a Google on idle cut off in Lycoming engines and you will find other sources describing this procedure and it's importance and possible causes/solutions to problems encountered doing this. Probably better than mine.

Roberta

Is it possible to safety the screw once the setting has been dialed in? Has anyone tried that?

robertahegy said:

You need to lean more at higher altitudes. When I land at airports higher than 4000 msl, I leave the engine slightly lean on landing. Taking off you also need to lean a bit. I'll pull the mixture out during runup to smooth things out prior to TO, especially places like Aspen or Leadville. The leaning runup is done at higher than normal rpms to make sure you don't lean too much and still have proper TO power.

Click to expand...

With our airports at 4200-4600' msl to start with, it's common to lean right after engine start. Lean before takeoff, and never full rich for landings (possible go-arounds). The power loss from being full rich is very noticeable, even though pilots from coastal areas don't seem to get use to the fact too quickly!

L.Adamson KSLC, U42

edit: I'm surprised that some POH's, manuals still suggest full rich for landings, while others will say adjust mixture as required for altitude, such as 3000'+ for density altitudes.

Mixture screw..

Hi Roberta,

What you say is correct, and in line with Lycoming recommendations. As is often the case, there is a fair degree of latitude. I offer Mahlon's comments as those of an acknowledged expert, not so much to illustrate my previous point, but to see where I was coming from. Best Rgds, Martin

"G'day Martin,
What you describe is what is typically too rich of a mixture setting. When the Idle is really set to a true 25 RPM rise the difference in operational smoothness and feel is almost unnoticeable to an engine that has the idle set at peak. However, if the engine is really much richer then that, but we think we only have, a 25 RPM rise, then leaning the engine at idle and off idle provides dramatic improvement in smoothness and feel. The key is to check the mixture at 7-800 rpm and lean the mixture very SLOOOOOWLY. If you can hear the rpm rise you have more then 25. If the tach shows 25 but you can here the rpm going up you are not seeing the true rise. In reality the reason for setting the idle with a small RPM rise is like running slightly rich of peak in cruise...that is the mixture engineer's would like to see and should provide the best acceleration and good operating characteristics
If you engine accelerates fine out of idle and it runs smoothly and also satisfactorily when it is cold out, your adjustments are just fine in my book. You obviously have a very good feel for the engine and how it runs and can make a determination as to what to do if it doesn't run at idle the way you want. But another bloke might not be as in tune as you are, and adjusting his engine by the book should produce a proper running engine at idle...... maybe not running as nice as yours but certainly adequate.
Good Luck,
Mahlon
1-800-624-6680 ext.305
www.mattituck.com "