Do these plugs look "lean" to you? To me the right plug looks a touch more lean than the left, and the left plug looks pretty well perfect.

Right plug:


Left plug:

Haha. That picture is mislabeled. It should say: "Unused plug, normal used plug, plug intentionally coated in oil".

There's a far better diagnostic picture floating around:


My plugs, frankly, look "Best" on that scale.

I'm mostly concerned with why the ring of the plug is black and sooty while the electrode, strap and insulator look perfect. I suspect the black on the ring indicates it's running rich at idle.

Don't be concerned with the ring, be concerned with the electrode and insulator.

The ring will get black and sooty from age and carbon buildup and maybe some burnt oil and other stuff.

If the electrode and insulator is black and sooty that's where it indicates a rich condition.


Your right plug does look like its in a leaner condition, but both seem "good".

I've always thought mine were a bit lean but I've come to wonder about using those old photos because they were made ages ago when petrol did not have the high quality additives and detergents, so they might look a little lean, i.e. not have that wonderfully perfect tan pixie dust but not be be lean.

Try this with the bike warmed up, in neutral and idling at correct speed, rev the engine to say 6,000 and immediately release the throttle. Apparently the engine speed should smoothly drop back to idle and stay there with no funny business. It should not overshoot idle.

Quote from: user11235813 on November 29, 2016, 02:35:23 PM
Try this with the bike warmed up, in neutral and idling at correct speed, rev the engine to say 6,000 and immediately release the throttle. Apparently the engine speed should smoothly drop back to idle and stay there with no funny business. It should not overshoot idle.

Yes unfortunately that's precisely the type of problem I am trying to sort out.

How quickly do plugs change their color?

Say in a hypothetical situation where you ride about 50 minutes at conditions that are too rich, and then finish the last 10 minutes where it's too lean.

Do the plugs reflect the average of all that, or just the last few minutes of the ride?

Looking at the plugs is only a rough indicator, good for indicating serious mixture/combustion issues not good for indicating exactly what's going on at various throttle positions across there range and under different loads.

O/P needs to get himself one of these......

http://www.gunson.co.uk/product/G4074/

http://www.frost.co.uk/gunson-colortune-kit-review

Quote from: sledge on November 30, 2016, 03:12:21 AM
O/P needs to get himself one of these......

http://www.gunson.co.uk/product/G4074/

I actually have one somewhere. Haven't used it in over 20 years. It's buried in some box of abandoned tools in my garage's storage loft where it's been for decades.

Probably more worthwhile to buy another one rather than spend the time digging up the one I have.