Spark Plug Difference

A

AlexBeckwith18

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Hey all!

Just posting quickly because i'm a little baffled and wanted to crowd source your knowledge. My right cylinder #4 has been acting odd and seemingly down on power. Here is a picture of the plugs from cylinder #1 and #4. The clean, heat bronzed one is from the #1 (normal acting cylinder).

Does anyone know as to why they look different, and what it tells you about whats going on in the cylinder? What I have done so far:

- Did a spark test, both are sparking
- Changed the mixture slightly with no noticeable difference.
- #4 spark plug smell like oil and fuel....

Any help is much appreciated.

Thanks,
Alex Beckwith
Yamaha Radian YX600

3ayKcQ6.jpg
 
There are plenty of charts online that could be googled that would tell you what the color of your plugs means.

Just google "Spark Plug Chart" and look in images.

I tried to add the URL of one to view here.. but it kept telling me it was to large.. -_-
 
Have you done a compression test?

How do you know the plug is sparking while in the engine under compression? Testing for spark while out of the engine is a good first step but I have had plugs that seemed fine until installed.

How did you change the mixture? Did you change just the problem carb? How hard is it to swap carb positions on the Radian to see if the problem follows the carb?
 
Last edited:
yup, compression test is in order :| theres not much fire happening in that one.
 
I am thinking that both of these are relatively new spark plugs.

The black insulator and ground electrode on #4 means it is firing (and is rich) some of the time, but that the rest of it is so clean and shows no heat markings suggests to me, "too rich to fire" most of the time - firing just enough under some conditions to make the insulator black.
 
That #4 is a new plug, not in the engine long and it is already carbon fouled. Agree with Greyghost about having a compression test. That doesn't just look like a rich mixture. You might have a cracked ring. Mileage of bike? Have you been revving it to the moon? The #1 looks lean, probably what #4 looked like before the problem. Have you noticed any pre-ignition ping? Detonation will definitely crack a ring or damage the piston.
 
FFS - The bike is 30+ years old, it could be anything from a plug cap/ignition wire, to carburetor jetting, to internal engine issue.
Checked the valve clearances in the last decade or so ?
Start from the beginning and don't overlook the simple stuff.
 
Hey Alex, IIRC you're in St C. If you swing by Grimsby I can help you look over some things. What did you do to change the mixture?
 
TK4 said:
FFS - The bike is 30+ years old, it could be anything from a plug cap/ignition wire, to carburetor jetting, to internal engine issue.
Checked the valve clearances in the last decade or so ?
Start from the beginning and don't overlook the simple stuff.
Click to expand...

If it's not rings, it's guaranteed to be the carb. Likely gummed, dirty and the slide is getting stuck.
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