When reading plugs, do you need to run it at full throttle then kill it or can you land, drain fuel, then run the carb out of gas before checking? I ran the fuel out my my motor (ran for about 20 seconds at 1/3 throttle) after the last flight of the season. My plugs are a pretty medium chocolate brown color on the insulator.

The most accurate "Picture" is: kill at full throttle & then "Read"---(you will need transmitter ignition kill capability)---

Silliness,
I cannot shed the feeling that you already know the answer.

Same here

Thanks for the sarcastic answers. I'm not trying to waste your time, just confirm my suspisions. The reason I asked is because I swear that someone once told me that there is a different place on the plug that you use to read low end. To me this plug reading business is PFM (Pure $#%$# Magic) anyway... thought there might be chance I was wrong. I often am.

Logging off.

I used to run at full throttle and just kill the ignition switch on my 250 two stroke years ago. That worked great. So I imagine if I ran my DA50 up to full throttle for 5-10 seconds and just flipped my ignition switch off, then throttle stick down, that would accomplish the same thing.

The oils you run can really change what you see - but - what you are really interested in is the color of the insuator porcilain.
However -if you simply make a quick run -you see nothing of real value -
There are lots of pics on spark plug info pages showing what typical results mean.

There is a general rule, that rubbish in is rubbish out. Since you rephrased the question to meaningful content, a meaningful answer is possible.
Very important is, that you run the engine for a significant period of time, before conclusive answers can be given. Many engine tuners insist on using a new plug for every analysis, lest the old plug hides the new carb settings.
having said that, these are the things to watch for, and only after the engine has been cut in flight.

1) the central electrode and isolator body.
these parts indicate plug heat range and mixture strength. The lower down into the body the discoloration is, the hotter the plug is. The colour itself determines the mixture strength. Think of colour in shades of gray, because fuel and oil can influence hue (shade of colour). If the central electrode itself looks burnt, the plug is way too hot, or there is too much preignition.

2) the earth electrode.
This can be used to judge ignition timing and compression ratio by the distance the colour travels toward the body. Halfway is about good. Too much means early ignition, too litle, and ignition should be advanced a bit. The electrode looks "baked' if the CR is too high. in this case, the central electrode looks weird as well, sharp edges may become rounded, requiring a re-dressing of the plug.
Prolonged lowe power running:
Central electrode glazing occurs when the engine is run at intermediate power too long, and then suddenly high power is asked for during a little period. The condensed particles are glazed onto the electrode before they had a chance to flash off by rising plug temperature.

Worn plug:
Dispite correct heat range, plugs wear out sooner or later. With every spark, a wee bit of material evaporates or melts, so bye and bye the plug looses it's sharp-edged appearance. Time to replace the contraption, and fit a new one.

Needless to say, that every now and then, the plug needs to be set at 0.5 to 0.6 mm gap (0.020 to 0.025" ) , or to ignition manufacturer's specification.

Plug reading has become more difficult since the introduction of oxygenated gas. Modelers have it easy since our engines are under a consistent load, we can accurately tune by ear. If the engine is somewhere between fourcycling rich and buzzing with detonation lean, you can be assured the plug will end up some color between black and white.

Any info how this gas affects plug readings? Or where these poor affected souls can get further info?
I inserted a map with reformulated gas areas in this post. This links to [link=http://www.epa.gov/otaq/rfg/information.htm]GOV publications about the clean air act[/link].

I found a [link=http://www.amiles.com.au/rmr/SparkPlugReading.htm]good link with plug charts for two stroke engines[/link].

Here is a pic of a plug with less than 1/2 gallon of 91 oct pump gas mixed 32-1 with Mobil MX2T running on 21x8 Mejzlic on JMBcan- 7200 rpm on the ground- The piston looks perfect -no scratching or marking or staining.
All in all about as good as it gets.
this oil combo leaves the metal body of the plug looking like it has been scrubbed clean but it is exactly as it came from the engine.
It will change as I run it more -but this is how a new setup can look- running properly.

I am one of the poor affected souls[:'(]

Hmm... sounds strangely like flying an IMAC/3D airplane... oh well.

Thanks for all the usefull info... much more info than I had on the subject.

Not like that.
consider low speed running much like your great-granddad runs a car, and then suddenly your son decides to hammer it.
Glazing in leadfree gas is a thing of the past I think.

@Dick:
My plugs look much the same The central electrode colour is much influenced by the oil type (Aspen all synthetic brew in this case):
This comes out of my 35cc engine after hauling duties:

looks identical to me -
watch that great grand dad stuff------
darn young whipper snappers ---

Your ignition has slightly less advance, as can be judged by the brown colour not quite running up to the shoulder of the ground strap. You may gain a bit power by adding some extra timing.

All of these engines shown are running to rich on the mixture. A proper heat range plug will be a tan brown colour on the centre electrode when set to the right mixture. You can put up a good high throttle run for five minutes, throttle back to idle, land and check the plug colour. It wont be running long enough at idle to affect anything. reset the cerb and repeat till it's running the right colour. Don't know why things are made to appear so complicated. Has nothing to do with ign timing.

Too rich?
slow advance?
yes to both
and it is intentional.
If the model were to be flown at full tilt and zipping along- it would be set a bit leaner also at our altitude (unloaded running)-I can run with more advance (4350 ft elevation.)
At present, on the 21x8 it is very responsive to throttle command from slow thru mid range.
The advance will be first change (increase torque) and then I will play with low speed needle -lastly the high speed
I want to keep the engine responsive at mid range power running.

I found better starting, overall throttle response and stable running throughout the envellope at a slightly rich mixture.
Leaner in theory may be better, but sometimes makes the engine a bear to handle, and not better behaved in flight. It also increases exhaust temperature considerably, which puts a heavy burden on the header to silencer coupling.
Also, the margin to a fried piston is so much smaller when running at optimum lean mixture [:@]

OK gents.
Keep the information coming.
I have one question.
I looked at the two plugs in the above post and was under the impression that the ceramic insulator should be lighter in color.
Is the dark color do to running a lower oil ratio?

The colour of the two pictures cannot be directly compared, due to lighting and camera differences. Also, Dick used Mobil oil, while I used Aspen fuel which is not gasoline, but pure alkylate fuel. Both oil types are fully synthetic Jaso FC class.
Like I stated before, it is more important to look for the shades of gray and the transitions on central electrode, isolator, plug body and ground strap, which tell the tale on heat range, mixture strength and ignition timing. Some engine tuners can even discriminate the idle mixture strength. (I can not)
In general, oil presence and oil type does make a difference in the plug colour, and oil content has remarkably little influence. This is not surprising, because so little of it is in the mixture, even at high mixing ratios. At high oil ratios like 1:20, the oil content tends to foul the plug sooner when the plug is of a cold type like in racing engines with engine cold. When the engine is up to working temperature, the plug is selfcleaning, and fouling does not occur anymore.
In our aircraft engines this is not the case, while we run medium heat range plugs that heat up very fast.

[] After a plug fouls, can it be cleaned and restored by soaking in Acetone or MEK for a couple of days ?

> Jim

It is a 4$ item, why spend a lot of time on questionable results? It can work on a fresh oily fouling, but normally only heat will burn off deposits well enough.