Your thoughts on sparkplug colouring?

[John Orchard]

I just thought I'd ask you guy's to see if anyone can confirm an answer.

The colouring of the sparkplugs on both my 2005 Yamaha YZ144 and 1984 Honda CR500 are strange, one side/half of the porcelain is a very light tan colour and the other half is a dry black.

The YZ runs full synthetic oil at 30:1 and the CR runs mineral based oil at 30:1.  I've tried various fuel types; BP 95 octane, United 95 with 10% ethenol & Caltex 98, all with the same result.

I originally suspected an uneven burn in the combustion chamber but the burn marks on the piston crown don't show anything uneven.

Then I suspected maybe a higher heat from the exhaust side of the combustion chamber burning that side of the plug cleaner?  Next time out I'll mark the plug when fitted to try and determine if it is related.

So, depending on what side of the plug you look at, my carburation is either slightly lean or too rich  :-)

Possibly the carb is too rich on one circuit, and too lean on another, and as I shut-it-down it starts to discolour the plug, but the shut-down procedure is not long enough to colour the plug all-over?

After my plug-chop, I am diving on the clutch & the kill-switch at the same time, and trying to keep the twist-grip at the same position, but I worry that the slowly decelerating engine is still bringing in fuel?

[pokey]

Girlfriends CB250 twin has that aswell. on both plugs and both on the inside

i put it down to the nice brown was facing the exhaust and the black was being shielded by the electrode.

her bike is running a tad rich but Im not concerned by it

[sleepy]

It's probably the incoming charge from the boost ports shooting up from the back of the cylinder cooling that side of the plug. You would have to mark the plugs position to confirm.
Plug colour is not as reliable with unleaded fuel as the good old leaded was, still worth looking at though.
I've found on some of the speedway car engines that I play with to look at the earth electrode with a magnifing glass and if the plating is starting to bubble then it is time to go a little richer. They are on methanol and turbocharged which is a little different to petrol 2 stroke.

[Slakewell]

I'm still learning all the time about two stroke tuning.
I always used to go with dark tan myself. New fuels and new oils have confused me. My mate has been doing some interesting stuff with a temp probe in the header looking for cooler combinations of fuel and oil.
There is some that work better than others and the new bio fuels are not always what runs hotter in fact some of the race fuels are far worse. Fully synthetic oils are not doing to well either. The older mineral based oils at under 30 to 1 so far run cooler.
There is some thought that the thicker oils help remove the heat and transfer it to the fins? 
Whilst the new stuff is OK with water cooling the old stuff oils might be better with air cooled bikes. Testing goes on. 

[bazza]

Over here all the fuel has 10% ethanol now to be trendy and green and it makes plug reading harder than it used to be

[FourstrokeForever]

Plug reads are so hard with unleaded fuel. If I see a light tan colouring, I tend to richen the carb setting a bit until I see a grayish to almost black colour. At least then I know that the settings are a bit on the rich side. Hey, I'll sacrifice some responsiveness for longevity every day of the week.

And as per what Slakewell has written, I have always suspected that synthetic 2T oils were running hotter than mineral. I came to the conclusion by the relatively short life span of spark plugs these days. Having read your post Slakey, I think I'm going shopping for mineral 2T for my smokers.

[Slakewell]

My mate has done all the hard work , I'm just joining in now it makes sense.

[80-85 husky]

im dubious about any plug color with unleaded. thinking about grabbing some avgas to get a plug color I can trust and be happy about.

Still on average I like a nice pink for my spark plugs but the paint comes off too quick....

[Lozza]

I just thought I'd ask you guy's to see if anyone can confirm an answer.

The colouring of the sparkplugs on both my 2005 Yamaha YZ144 and 1984 Honda CR500 are strange, one side/half of the porcelain is a very light tan colour and the other half is a dry black.

The YZ runs full synthetic oil at 30:1 and the CR runs mineral based oil at 30:1.  I've tried various fuel types; BP 95 octane, United 95 with 10% ethenol & Caltex 98, all with the same result.

I originally suspected an uneven burn in the combustion chamber but the burn marks on the piston crown don't show anything uneven.

Then I suspected maybe a higher heat from the exhaust side of the combustion chamber burning that side of the plug cleaner?  Next time out I'll mark the plug when fitted to try and determine if it is related.

So, depending on what side of the plug you look at, my carburation is either slightly lean or too rich  :-)

Possibly the carb is too rich on one circuit, and too lean on another, and as I shut-it-down it starts to discolour the plug, but the shut-down procedure is not long enough to colour the plug all-over?

After my plug-chop, I am diving on the clutch & the kill-switch at the same time, and trying to keep the twist-grip at the same position, but I worry that the slowly decelerating engine is still bringing in fuel?

Piston colour is far more important than the head, the head colour is more from the head itself. Plug readings from unleaded are easy if you know what to look for, that is a brown soot ring at the top and bottom of the insulator. Then your burn back on the J strap.Can you post a pic?

[supermotomc]

So get a small magnifying glaas your looking deep within the plug at the  central electrode at the base you should see a dark ring 2mm in dia thats ok heat range  then look to the tip of the central electrode right on the end you should see a burnt ring any wider that it too far advanced less too retarded ! Basics !

[Ted]

I think white is perfect for a spark plug colour, with either black or blue writing...I'm not fussed

[RD]

 

[David Lahey]

im dubious about any plug color with unleaded. thinking about grabbing some avgas to get a plug color I can trust and be happy about.

Still on average I like a nice pink for my spark plugs but the paint comes off too quick....

avgas is no good for getting the jetting right unless you are going to use it all the time because it requires different jetting settings to modern unleaded

[80-85 husky]

that's the end of that idea then...

the last lot of jetting i did was basically by feel as the plug didn't seem to change color regardless of jet changes. so it was jet up to a blubber and back of a size or so to clean it up. seems to be ok

[Marc.com]

that's the end of that idea then...

the last lot of jetting i did was basically by feel as the plug didn't seem to change color regardless of jet changes. so it was jet up to a blubber and back of a size or so to clean it up. seems to be ok

I am into the seat of the pants dyno or better yet a real one ..... make one small change at a time, ride it work out if it feels better then quit while you are ahead. One needle notch can make all the difference in the world and you would never pick it up gazing at spark plugs.

Ethanol in the fuel means the fuel ages and fast and really you may as well be tossing chicken bones in the air to guess the AFR. Ethanol is on the same hate list as cycle lanes, Greens trying to control the world with shitty science.