Would appreciate assessments of the "tune" of the engine this plug was in.....these are un-retouched, no color alteration, white balance "normal".

I'd read it as just slightly lean.

It's really hard to tell because you are not showing the bottom of the insulator where the reading is taken.

Without knowing how much fuel has been burned by the plug I would also say just slightly lean. Plugs in a correctly adjusted engine will, many times, look slightly lean after only a couple of tanks. If this plug were in my engine I would not be alarmed at all, I would just give it about an 1/8 turn richer and check it again after a couple more runs.

Jody

Looks real good, perhaps very slightly lean, but hot. If it came out of a twin it could be the plug farthest "downwind" from the intake rotation. Heat's not moving away as much as you might like it to.

I am very appreciative of all the opinions shared thus far! Please keep 'em coming.
Pat - single.

About 2 hours on the plug.

If that is 2 hours of running on a fully broken in engine I would be tempted to leave it alone. But Bob, I have read many, many of your posts, been to your website and I am confident you know how to adjust an engine and are a fair judge of carbon, have you had a problem or are you just testing the RCU'ers?

Jody

Thank you, no problems, not "testing", because I am not that expert at all with these things.

Mainly, I wanted to hear a consensus of opinion about a visual "point of reference".... so often these tuning threads describe things, but we all know a picture is worth a thousand words. I'm trying to add to my knowledge base to share based on the judgements of folks who share their views on it. There is a LOT of experience out here....and, no pun intended, there can be "many shades of grey (or tan)" to this engine tuning stuff.

Truthfully Bob,

It looks very much like a 50-1 plug, synthetic, that's in a very well tuned engine. I've seen a lot of plugs with 25 and 50 hours on them that came out of engines "flow tuned" on a bench that looked almost exactly the same. That engine appears to be running in an rpm range that's above the middle most of the time.

I would be quite happy to see my plugs look that good.

Well said! My opinion is that you likely have a fine running engine that needs little more than a birds eye view.

Jody

I read the plug just about right on. I also think she has been run hard some times. I think that is what makes tiny white specs on the dark metal threaded ..end of plug. Capt,n

At a first glance I said a little lean. I think it should be a little tan or light brownish.

I just plugs out of four of my engines, I think the MT engines are tuned the best, left to right:

3W-75 I just got this a couple of months ago, original plug, flown mostly 3/4 throttle, 2 gallons through it since I got it. Bell Ray 50:1, 26x10 TBM 5460rpm, NX26x10 5800rpm seems in good tune.

Brillelli 366GT Pennzoil 50:1, flown mostly 3/4 throttle 3 gallons on plug. This engine is hard to tune, no-matter how I tune it it runs great. TBM 22x8 6660rpm, Vess22A 7200 rpm.

MT62 Pennzoil 50:1 flown 7/8 to full throttle, 4 gallons on plug. It exactly matches the Brillelli in rpms with the same props, great running.

MT50 Pennzoil 50:1 Flown full throttle 95% of the time, 3 gallons on plug. BME 20 3D A & B, or a 22x8, I just forget what it turns, runs great.

Those are great pics, Rich. Thanks for adding to our intel.

Bob,
Look at this picture. The black ring shows the tune


Edit.
the isolator tip shows plug heat grade (if mixture is OK)
It is where the isolator meets the plug body that shows mixture strength. Can be seen using a maglite
The plug body rim has importance as well. If oily, the mixture is too rich. Black is OK
The central electrod shows ignition timing. Soot should creep up to the tip. If not, ignition is too early (advanced)
Here is a picture of some plugs I disassembled. Just for the pictures. In real life, disassembly is not needed most of the time

Plug 1 is slightly lean, as indicated by the head temperature.
plug 2 is slightly richer, the black ring still is not as high as 1/4 isolator length
plug 3 is too rich. The black has crept up to 1/3rd isolator length.
plug 4 is too rich, but heat range is OK (champion DJ7Y)
Plug 5 is too lean (no black ring) It also is too cold (champion DJ6J black nose)
plug 6 is right mixture as shown by mixture ring, but too cold.

Pe,
What black ring??? Very interested in this info right now. I had ignition problems with a DA 100 this past weekend that has ~300 flights on it. I pulled the plugs and was surprised to see plugs that look like Soarrichs plug that is second from the left in his picture. Looks rich to me but the engine seems to run smooth and fine??? I do fly it mostly at 2/3 throttle and below. I usually run Amsoil Sabre
about 70:1.

Thanks,
Steve

I have a question. Is it best to fly at least 4-8 min at 80%- 100% throttle and then shut engine down in air and glide in to get a perfect reading? Or on a test stand...with a quick shut down? Just wondered. Capt,n

Your plugs may be a tad cold, and your tune too rich. The engine may still have great power, but plugs foul in time if they cannot burn themselves clean.
In my picture there is the narrow black mixture ring, where the isolator meets the plug metal housing. The tune of the pictured plug is slightly lean, but that is the best tune if cooling is OK. A wider black ring is better, but it should not exceed 1/4 of the isolator length.
If in doubt, dismantle your plug to check how it looks. Plugs are dispensable, engines are not.

The black ring Pe is referring to can best be seen with a coddington magnifier. (At least that's the best way without cutting the plug apart like Pe did here.) It has a built in light that can illuminate the very bottom of the insulator and a magnifier that allows a good view of the base of the insulator where the mixture ring will be seen.

P.S. A coddington magnifier is what a Doctor uses to look inside your ears and nose etc.

Since your asking questions I will throw in my .02 cents worth. If my plugs looked like that and I had good baffling, no sagging on extended WOT runs, I would not worry a bit.
Although I "might" richen it a tad, unless the richening muddies up the mid range, then I would not touch anything.
I tend to run a richer oil mixture than most and "usually" have good baffling with low pressure areas for good air extraction. If I run a tad lean I usually have no problems anyway and my low and mid are very clean.

I have access to those... great idea, will research that further! Thanks!

Hmm. I just cut the plugs to cure my own ignorance and curiosity. The lessons learnt were quite iluminating. When you know what to look for, there are many ways to skin that cat.
In the end, do not forget to examine the piston top, piston bottom and skirts . They all contribute to understanding how well the engine (as a person) feels. I mean, the big picture that is made up of ignition advance, cooling, plug choice, fuel grade, carb tuning, oil type, and oil / fuel mixture.

Pe

Could you elaborate on the soot on the plug in relation to the timing?

I think, that TSR has the best overall picture made that I have ever seen.

Thanks Pe, that really helps.