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MG MGA - Spark Plug Colours

Still plodding through archive MGCC Safety Fast magazine articles, converting hard copy to html. I came across the following paragraph about the use of unleaded fuel:

"........Spark plugs used to be a great help in mixture settings as did tail pipes on exhaust systems with their light or dark colour helping to identify weak/rich mixtures but not any more. Plugs are often black on unleaded fuels when the mixture is rich or lean, as are exhaust tail pipes."

True or false?

Steve
Steve Gyles

I'd say false Steve. Insulator should be a light tan colour but sometimes I have seen a brick red colour. I think this is caused by certain brands of fuel as it seems to come and go. Anyway, bleached white is too lean and black is too rich.
Lindsay Sampford

The same guy also made this comment (the car in question was an MGC):

"...I have found that with the use of unleaded petrol, although the engine was in tune, a much improved performance can be gained by the change of the spark plug type used. I discarded my original NGK BP 6ES plugs which had served me well with leaded fuel, for a set of NGK BP 6ES Copper core. These have made a total difference to the running....."

How would copper core make the difference?

Steve
Steve Gyles

I think it's true with regard to exhaust tail pipe colour.
J Bray

Steve in another life as a service mechanic with Ford I found a new set of plugs always showed an improvement for a while. Must be the lower resistance of new plugs. We also used to file the electrodes nice and flat and shinny during a tune up when reusing the origonal plugs. In my 1500 A I run Iridium plugs [ with 40,000V coil ] because they need about 5000V less to fire. Lets me open the gaps to
32 thou for a longer spark. Engine pulls [3.9 diff ] cleanly and strong all day. Sean
S Sherry

I thought all NGK BP 6ES were copper core. Supposed to be one of the reasons that these plugs have a broader, more forgiving heat range than other plugs.

My experience has been similar to Lindsay's.

--Jack
JM Morris

Jack

It is worth mentioning that this archive document was dated 2001, so the NGK design may have changed slightly since then.

Steve
Steve Gyles

Leaded gasoline was outlawed around 1980 here in Canada. The spark plug colour charts still hold true.

Ralph
L Poupard

This thread was discussed between 20/12/2011 and 21/12/2011

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.