Spark plug readings

[Makotosun]

Just saw this on a Facebook group post and thought it was interesting. Can we have an expert weigh in as to how accurate/useful this may be?

Posted without warranty, attribution or comment. Looking for feedback!

[hodakagirl]

I like that it has pictures. I'm still getting the hang of plug reading. I found this on another forum I'm on, and it seems pretty helpful as well. Not sure of the original source:

[Makotosun]

Nice!

[Bill2001]

Good diagram. Which other forum was it found on?

[hodakagirl]

On the modern vespa forum, in the not-so-modern section. I kind of divide my time between here and there lately.

[Bullfrog]

I sure can't take issue with either of the posted photos/diagrams. But I would add a caution.

Unless you are a very experienced tuner, who takes care to follow the proper procedures for "taking a plug reading" -- or you are a very experienced tuner who can reasonably interpret the condition of a plug which has been removed from an engine at any old random time . . . please (PLEASE) don't suddenly start making major engine tuning decisions based on plug readings simply because you have the two photos/diagrams for reference.

Please don't forget that a "plug reading" is influenced by ALL the factors which influence combustion. Oil mix, oil type, gasoline type and grade, ignition timing, compression, cooling effectiveness of the head, spark plug type, make and heat range, duration of run time on the plug, type of engine operation during the duration of the run time on the plug, jetting, presence or absence of crankcase air leaks, etc, etc, etc.

Plug readings are helpful - but don't forget the other things you can also review (see list in previous paragraph). Are those other things "right"? (many of them are "binary" in nature - ie, "right" or "not right" - and are therefore much easier to interpret) Plug readings (for most of us) are so heavily "analog" that interpretation is difficult. (ie, this part of the plug looks good, but that part doesn't looks so good, and this third area? Well, I just can't tell. What should I do?) I guess the point is . . . the photo and diagram won't make any of us an expert on plug readings . . . so don't behave as though they do.

Ed

[hodakagirl]

Good point, Ed. I'm certainly not an expert at plug chops or tuning. Just wanted to pass on some info that might help others. Thanks for the words of caution.

[Makotosun]

Good point, Ed. I'm certainly not an expert at plug chops or tuning. Just wanted to pass on some info that might help others. Thanks for the words of caution.

Thanks Ed - Agree with the above. As you can see in my first post I was asking for you to weigh in . . .

[Bullfrog]

Which is why I weighed in. Just wanted to take some time to "measure" my words.

Ed

[taber hodaka]

If you tune by plug color, you could have engine failure before your testing is complete. Tune it by sound and performance. I read the plug to see if I am using the correct heat range plug after it is tuned. In the day I considered myself a good tuner, Harry was among the very best. Clarence

[hodakamax]

Just weighing in here and agreeing with people with lots of experience. To me, plug reading confirms how well you've tuned so far. Pretty basic at first, start rich and work toward performance. With an air cooled two stroke we must also consider lubrication and that the intake mixture is part of the cooling process. Like all things in life, the more you do things, including failure, do you get experience and a feel for what you are doing.

Also worth mentioning, however obvious, is to do your performance testing with a fresh plug so you won't be reading what happened in the past.

I especially liked Clarence's advice about using more than plug color for tuning. You could destroy the engine before figuring out what the first reading meant.

Maxie

[Hydraulic Jack]

I don't tune by plug color and never have, but I do check plug color if I change jetting, and sometimes to double check something I hear or feel. Not a primary guide to tuning, but useful when used carefully in combo with all other tuning tools, or for fine tuning for conditions.

Bottom line is the color chart isn't wrong. The question is how you use it.

[taber hodaka]

Good point. -------Clarence