I'm pretty sure this will be unanimous. My ZDZ 50 NG quit while buzzing around at or near WOT for a few minutes. I thought it was due to a lean run. Check out the plug. It was never run after it quit up in the air (dead stick). I think it looks lean.

that is the cleanest plug i have ever seen out of a gas engine.i don't like to see mine any lighter in color than a dark gray,better yet a light tan in color.but i will put money on it though the reason it stop was due to a lean run.but i am no expert just a guy with a wrench and a hammer.

Hi Joe

I also think it is lean, the last picture shows up that effect.

Yeah a clean plug is not good in this case. I think it's so clean because it was so lean. Not sure what made this engine go lean. It was running great and then all of a sudden this issue pops up. Think I may have an air leak in the engine some where?

...mm is hard to say, Joe an engine flame out is one of the hardest think to figure out.
Once upon a time I had all the good stuff installed on my airplane to monitor temperature and rpms (I had an eagletree data logger), even having those parameters recorded I could not figure out what did cause the flame out on my BME110.
Don't feel bad, just about all the engines I have opperated have flamed out on me, for the 50% of the events I think I know what happened the other 50% is a total mistery to me.

Engine cooling? I know that the head cylinders is fully exposed and that may account for a good air flow; however some summer days in Wisconsin can get really warm as far I recall.

Hi Alejandro. I took the carb side plate off and didn't find too much dirt in the screen when I cleaned it. I did notice that my zip tie on the fuel line barb was very loose. That might have been letting in air. I put a new zip tie over the fuel line on the barb. Hopefully this will fix the lean condition. I should probably richen the needles but they have been working very well at the setting they are at (1.75L/1.75H).

Anyway I'll take it to the field an run it...fly it and hopefully I don't wreck the plane in a dead stick. It has survived many dead sticks but one of these times I may not be so lucky.

A very short lean run due to some mishap before the engine quits will be impossible to tell from the plug. Let guesswork be guesswork. You need a decent run to get a good plug reading.

Hello Joe. Looks like it was the day for this. I had a flame out on a very reliable 3W 55 yesterday. I was at the bottom of an inverted flat spin. I always bump the throttle to keep it cleaned out but this time it just quit. It was a very warm day, with fairly high humidity here in Ohio. I wound up going off the end of our runway which drops off on rocks and rough ground. The front of the engine box failed and took the cowl with it. Bent a wing tube, but not a scratch on either wing! Gear is perfect, and didn't even break the prop, even though the engine came completely loose. No damage to any covering. I'll fix the front end and be back at it soon. It was my Aerotech Yak. No joy.[]

The best way to tell is replace the plug and fire the engine. Run it to full throttle for about 1 minute and cut the ignition at WOT. Then check the plug to determine your tune.

From what I can see from the pictures, that plug does not look like the engine has been running lean.

I think it looks lean. If the color doesn't show up well in the pic's, I can tell you that it's a light gray and should be more of a light brown or dark tan. The plane was unloading a lot due to high air speed, I think it was running lean. I usually don't run WOT so I think that's why it showed up. Also I think possibly my fuel inlet was letting in air. I'll know next time I fly. I zip tied the fuel inlet so hopefully that makes the engine run more rich.

To check out lean setings, look at plug #5 in this picture. The plug itself is too cold, and has been set lean to obtain a brown nose, which of course never would happen. Look at the missing black mixture ring.

pe, are those same pictures available at higher res on your website? It's hard to see them here.

Edit: nevermind, I just saw your site link on the other spark plug color thread. Very scientific plug reading info. I like it.