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I pulled the plugs and found they looked like this:

This was not a proper plug chop, I was just checking the valve clearances. The plugs are NGK BP7ES and have done about 5,000km. I live in the country so 90% of my riding is at 100kph hence the cooler plugs. I use 95 octane unleaded (mostly Caltex). New pistons and valves about 7,500km ago, carbies pretty much untouched in the 70,000km I've done on the bike, the bike starts instantly and runs really well.

What's going on here?

Ray
'86 R65

raypond wrote:I pulled the plugs and found they looked like this:

This was not a proper plug chop, I was just checking the valve clearances. The plugs are NGK BP7ES and have done about 5,000km. I live in the country so 90% of my riding is at 100kph hence the cooler plugs. I use 95 octane unleaded (mostly Caltex). New pistons and valves about 7,500km ago, carbies pretty much untouched in the 70,000km I've done on the bike, the bike starts instantly and runs really well.

What's going on here?

Ray
'86 R65

Did you replace any O rings in your carbs with a red one?

Is one side of your tank getting rusty?

Verrrrry interesting!

Nothing red in the carby that I know of and nothing in the carbs has been changed in years. If there is rust in the tank wouldn't the cross-over pipe spread it to both cylinders? I have used copper-based anti-seize on the plug threads but it's a different colour, shouldn't have got into the cylinder and surely would have burnt off by now if it had. I agree with you : Verrrrry interesting!

Ray
'86 R65

Used to see red plugs many years ago on certain types of fuel,back when additives were all the rage....Caltex Boron etc.But that would be all plugs,not one.Deposits on the porcelain are usually additives,in oil or fuel....inlet leak?

As the engine seems to be performing OK maybe you could swap sides with the plugs and go for a run then have
another look?

Oil is being burned in the cylinder with the red plug. either blow by, intake valve stem or crankcase vent oil.

raypond wrote:If there is rust in the tank wouldn't the cross-over pipe spread it to both cylinders?
Ray
'86 R65

I'm pretty sure that was ZM's little joke, at least, it should have been meant as a joke.

George is right: it's gotta be oil. Not enough to foul, just enough to color, but, regardless of the source, it will get worse.

If the red color bothers you, try switching oils

The oil theory sounds right. Is there a simple way to determine if it's valves, rings or breather? Apart from the red how do the plugs look otherwise - hot, lean, just right?

Ray
'86 R65

raypond wrote:I pulled the plugs and found they looked like this:

This was not a proper plug chop, I was just checking the valve clearances. The plugs are NGK BP7ES and have done about 5,000km. I live in the country so 90% of my riding is at 100kph hence the cooler plugs. I use 95 octane unleaded (mostly Caltex). New pistons and valves about 7,500km ago, carbies pretty much untouched in the 70,000km I've done on the bike, the bike starts instantly and runs really well.

What's going on here?

Ray
'86 R65

I see the opposite problem. The white plug has more deposits than the red one. If it was oil you would see deposits on the red one. White is not a normal color (too lean), tan, light grey or light brown is ideal. I've seen dry reddish brown plugs on some of my best running machines. Some fuel is dyed red. I think your white plug may be a tad lean or there is a slightly uneven spark.

Actually, Matt has a good point. I really only looked at the "red" plug because that was the one that was asked about in the title. He's right that there are more deposits on the white plug, and it looks too lean besides. That does seem to be the one you should be more worried about.