I have read about the identical problem from others and I have tried the advice given to them but still the problem persists. Please offer your advice (Graybeard) are anyone else. Follows are the facts:
1. engine is OS FS91 that I have just adquired.
2. engine had not been run in 3 yrs but was kept in after-run oil
3. engine top-end and bottom-end transition running is excellent
4. engine idles great when glow ignitor is on plug
5. once ignitor is removed, the engine runs approx. 10 seconds and dies suddenly without a fade
6. low end needle has been adjusted both ways and no difference
7. hi end needle has been adjusted correctly
8. fuel tank is new but checked out thoroughly
9. 2 new OS "F" plugs have been tried with no effect
10. engine has been run 20 minutes with ignitor installed on plug at varying speeds
11. the fuel used works great on another OS FS91
12. It was suspected that after-run oil was fouling plug since engine is mounted inverted but no longer believe it
13. fuel is 15% wildcat
14. the carb was stuck initially but freed-up
I am beginning to think that the answer is to provide battery power to plug always during flight or possibly carb has debris at least partially fouling carb and it may need cleaning or just perhaps more run time. I appreciate your ideas and advice.....Wayne

At what RPM is the engine idling with the ignitor on it? Have you tried to increase the idle RPM a little to see if it will idle if it's allowed to run a little faster? It truly sounds like you're trying to get it to idle too low. Another thing to try is to change to a heavier prop. Sometimes the added flywheel effect is all that's needed. Hope this helps.

The drop in rpm or quiting after the glow igniter is removed is an indication of a rich engine. An inverted engine will be more likely to have problems in this areaas any liquid fuel that gets into the combustion chamber will drop on the glow plug and extinguish it.

First step is to start with the manual initial settings on both needles. Adjust the high end for maximum RPM then go rich by 300 or so RPM. Now set the throttle to the slowest setting that will keep the engine running. Leave the engine at this setting and then slowly, an 1/8 turn at a time removing the screwdriver after the turn, lean the idle for maximum RPM. Go back now and re adjust the high end again. Back to the low end and repeat. This time, the idle speed should be slower this time.

Now the transition. With the engine running at idle, slam the throttle full on. The engine may blubber and gain RPM (to rich on the idle) or just die (to lean on the idle), or instantly jump to the throttle, just right. Depending on the reaction make your adjustments in baby steps, 1/16th turn at a time and see what the results are. Adjust past the peak so the transition changes from rich to lean or the other way around.Then go back a 16th turn to the good side. If you don't over adjust, you will not know where peak performance is.

I was helping a guy out with his engine a couple weeks back. When I got near the peak, he was pleased and declared the tuning good. Ikept going until it was right and there was a huge difference in response and idle.

Iwouldn't try to run below 2300 rpm on the idle with the inverted engine.And it may be that you need and on-board igniter that kicks in at 3500 or so, but that is a last resort. Try tuning it out first.

Don

When I acquire a used engine the first thing I do is take it apart and inspect everything then clean it. It is sounding like you have crud in the low end of the carb. If it was gunked up and not working when you got it then that would be a good clue. If nothing else, remove the carb and soak it in alcohol or carb cleaner for a while, take it apart and clean it some more. What happens if you flip the plane upside down and remove the igniter?? Does it do the same thing or does it keep running? It could be a fuel tank location problem but it sounds like hardened Castor in the carb. Keeping heat on the plug isn't an answer, it's a band aid. I have run a lot of inverted .91s without a problem, the engine doesn't know it's inverted. With a used engine I use a starting stand and run and tune the engine while it's on the stand and not in the plane. My stand has a Velcro strip that holds the fuel tank so I can set it up correctly with the engine. If it runs well on the stand and not in the plane then I start looking at the tank location. From your list everything sounds OK. For engine cleaning I have a sonic cleaner, something I found that my wife used for cleaning her rings and what not. She hasn't missed it yet and it's what I use to clean my stripped down carbs and parts. Compressed air is also a big help. You know it's in the low end. If someone has taken the engine apart the cam may be out of time?? Take a look at the cam gear and make sure it is in correctly. I'm just shooting in the dark not having the engine in hand so these are just ideas I would have done. It's something simple but it's up to you to locate the problem.

Okay ! thanks for all the inputs. The engine will idle fast (I am guessing maybe 3000 or so rpm) the idle speed is much faster than my other plane with the same engine. However, the fast idle will still not cause the plane to move on the runway but believed to be fast enough to cause problems during landing. A tachometer has been used to adjust the idle and top-end running, I am not sure of this but I believe that 2300 was the target for idle. Realize that the engine will hold 2300 while the ignitor is connected but only briefly when the ignitor is removed. The prop size is 14X6 which I thought was a little small as my other plane uses 15X4. I am going to remove the carb and immerse in carb cleaner. I believe that to be the probable cause as the plane was running great 3 yrs ago on that prop and all of the initial carb needle settings. The concern about the cam gear timing is over my head (out of my knowledge spectrum) so that one will have to go to the bottom of the priority. The other band-aid is to take the plane off at fast idle and then just before touch-down to cut the trim and let the engine die to land. I have done this in the past but it is a last resort. I will make a copy of all responses and mull over them...again thanks Wayne

There are books that will show you how to do things to both 2 and 4 strokes. If it was running good before it was put away then there is no problems with the timing. Taking apart a carb and putting it back together isn't very hard, you do have to remember what you are doing and in what order it goes back together. Just a common sense thing.