7 replies to this topic

[decampos]

Hi Everyone. Just put some new plugs in. Anyone want to have a go at reading the condition of the old ones? I'm a real duffer at this type of thing.
Cheers

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[Big_Adam]

Far too lean, rich the mix a flat or two. Get a colortune.

[Phaeton]

Far too lean,

You Reckon??

rich the mix a flat or two.

As much as that??

Get a colortune.

Definately.

Alan...

[Big_Adam]

Far too lean,

You Reckon??

rich the mix a flat or two.

As much as that??

Get a colortune.

Definately.

Alan...

1, yes (Mr Vizard and hisbig yellow bible)
2, Flat. One flat of the jet needle assembly adjuster nut.
3, they are handy.

[Silicon Skum]

Yup, they show lean mix.

Follow the advice above, it's spot on.

SS

[Sprocket]

It all depends if the plugs are the right temperature to start with. If its a hot plug then they will show up as lean, if its a cold plug it will show up as rich.

Personaly that doesnt look too bad., i dont think theres anything wrong with it, if anything its a little rich with a hot plug. You have to remember that this is unleaded fuel so the charts you find in old books and haynes manuals do not depict what you will see correctly.

Top marks for taking a picture and asking the question. I dont know how many times i have asked people what colour the plugs are and got no response, yet they still persist in asking questions as to whats wrong with their engine.

[decampos]

Hi guys. thanks for all the advice. With lean looking plugs changing to rich when left to cool, it sounds like I should buy a colortune.
Cheers

[Silicon Skum]

Hi guys. thanks for all the advice. With lean looking plugs changing to rich when left to cool, it sounds like I should buy a colortune.
Cheers

by "hot" and "cold" plugs, he means the temperature the tip of the plug operates at during the combustion cycle, not the temperature of the plugs compared to background room temps.

regarding the "temperature" of plugs, If the tip gets too hot it can fire off the air/fuel mixture at the wrong time and this can cause detonation and / or pinking which could put a hole in your piston. If it gets too cold it will not burn off the carbon and fuel deposits on it's tip and the plug will foul up (stop working) which is not good either.
The heat range of a spark plug is controled by the length of the center electrode. A longer one is hotter as it takes longer for the heat to flow through it into the cylinder head. The cooler plug has a short center electrode, so heat is removed faster.

A higher compression engine should have a colder spark plug than a lower compression engine, this is because of flame temperature and overheating the plug.
The numbers on the side of the spark plugs give information on the plug, the higher the number, the "colder" the plug is:

Such as:
BPR6ES (a common NGK plug for twin point minis) - the '6' is what tells you the temperature of the plug.
BP7ES is a colder plug
BP8ES is colder still.

SS