What can you tell me about my engines by looking at my sparkplugs?

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BuckMKII

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The plug on the left is the original Champion CJ6Y taken out of my Echo CS-510 chainsaw. I purchased the saw new in 2003 and I have used it since then to cut firewood and clear some of my property. The saw used echo powerblend oil at 50:1 for the first 6 gallons of fuel it used. Since then I have used Mobil1 MX2T/ racing 2T at 32:1 ratio. The saw has the muffler baffle, spark screen and deflector removed.

The plug on the right is a two year old Champion CJ6 that came out of of my Stihl FS88 string trimmer. I got it second hand from my step brother who has a landscaping company. He used it for 2 years before I talked him out of it. The trimmer is at least 15 years old but it still runs really strong. It has used various oils over the years but in the last 7 or 8 years it has used the same Mobil oil mix as my saw. This trimmer gets about 40 hours of use a year because we have a long grass cutting season here and I have a lot of trimming to do to maintain my property.


I checked my Echo owners manual and it said that the saw takes a RCJ6Y plug but it came with a CJ6Y plug from the factory. I just replaced it with the resistor plug.

My Stihl dealer said that the trimmer needed a CJ8 plug and I used that to replace the CJ6 plug it had in it.

By looking at these plugs does it look like the saw is running too lean and the trimmer is running a bit too rich? When I did a muffler mod to the saw it was running too lean and revved up too high. I adjusted the high speed needle but it may be running a little bit too lean. The muffler mod really did wake this saw up from stock.
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Rich on the right and a tad leaner than "I" like on the left. I probably run my engines a tiny bit richer than some.
When I get home I will see if I can post a nice plug reading chart I have. One of the best ways to tell is by looking with a magnify glass at the base of the porcelain, the size of the black ring will tell a lot.
 
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Both plugs look to be still usable, little wear. As far as the color goes, did you shut the engine down hot. The plug from the trimmer could just be from idling too much.
 
The one on the left looks pretty good. I like to see the color be a kind of brown paper bag type of color. It doesn't look to be far lighter than that.

Bob
 
Both plugs look to be still usable, little wear. As far as the color goes, did you shut the engine down hot. The plug from the trimmer could just be from idling too much.

I do switch the saw off when I an done cutting so I guess that is shutting it down hot. The trimmer does not get idled too much, only when walking a short distance to trim a new area. It is ran between 1/2 to full throttle depending on how tall the weeds its cutting.
 
trimmer plug looks rich, you can see carbon/oil deposits around the rim. Put it back in the trimmer, warm the engine up, then run it wot for a bit, then hit the kill switch. See what it looks like then. I'll bet you need to lean it out a tad
 
He says his saw already has a muffler mod and he did richen it up a little. I would say the left plug looks pretty good could maybe use a little more fuel. The one of the right is pretty rich but not to an extreme extent. I would lean out the trimmer a little and see how things go
 
He says his saw already has a muffler mod and he did richen it up a little. I would say the left plug looks pretty good could maybe use a little more fuel. The one of the right is pretty rich but not to an extreme extent. I would lean out the trimmer a little and see how things go

Or, if the mixture is close to where he wants it, he could go a step colder on the spark plug.

It's hard to get in trouble going too cold with a plug.
 

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