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MG MGB Technical - plug color

...I've been doing soon fine tuning...and reading the spark plugs...and the car ('74-99,000 unrebuilt miles) is running great...and the plugs are slightly sooty while the electrode tip and insulator are brownish white...which seems correct...Any comments?...
Pete

idealy, the plugs should show a greyish/white colour, that indicated complete and clean burning of the fuel.

How long does it take, (from putting new or cleaned plugs in) before they turn the colour you describe?

I have about six sets of plugs that I've gone to cleaning , rather than replacing with new ones.

What you describe does not sound "serious" and as long as performance -- starting and running aren't affected, I'd say not to worry. One Chilton book suggests it could be some additive in the petrol you're using. But, with all things, if it ain't broke don't fix it.


glg
glg

Pete,

Assuming a stock USA engine in good mechanical state, stock lucas points and dissy, stock lucas coil, conventinal high tension wires, state of tune and timing of your engine, stock carb/s filters and needles as your base line. We need to ask under what conditions are you testing? And, what type and heat range of your plugs are you runnig?

I would expect to see a chocolate/brown/grey color on the insulator with grey tip for above conditions. White insulator (to me) might be wrong heat range of plugs (for your driving conditions), carb mix/needles too lean, or too much ignition advance. Does the engine 'ping' under load in top gear up hill?

During my early years, riding motor cycles reading spark plugs is a real science. Right, or wrong we would test over a controlled distance, slight hill, proven ignition system, new plugs of the proper heat range and gap, top gear, and cut ignition at a set RPM and distance. Re-jet carb/s, adjust ignitions until we thought we had it right. To that end, we believed we knew what we were doing, had a lot of fun, and repeated the practice after every race to see if their were any more power we could find.

Regards,

Larry C. '74 B/GT

Larry C '69 Midget

Pete The colors you describe are pretty right if they have just been pulled out of a normal driven vehicle "a bit of highway, a bit of town and a bit of general". Even with everything spot on you will only get a perfect color with new or at least clean plugs and driven under ideal conditions. With the introduction of ulp reading plugs is a little harder. Denis
DENIS4

One other thing to remember is as the weather warms, don't ride the choke quite as long. As the car becomes drivable start reducing the amount of choke.

I agree as noted that unless your examining the plugs after a prefect start, drive to 50 - 60 turn off and coast to a stop with the engine dead you aren't likely to get that perfect tan color.
Gene Johnston

"don't ride the choke quite as long"

Go by the temp gauge and learn how soon you can start pushing the choke back and how quickly. They are all different, my roadster needs full choke to start but then pushed back half-way immediately, then bit by bit further back until about mid-way between C and N it's fully back. The V8 needs full choke to start and for the first few seconds, then gradually pushed back to nothing again by about mid-way between C and N. The difference may be due to the HS carbs on the roadster and their main-jet enrichment, whereas the V8 has HIFs with a separate enrichment valve. Remember the first 1/4" should be fast-idle and no enrichment, so can be safely left for longer.
Paul Hunt 2

The car runs very fine...only needs a moment of choke to start...thx for all the posts...I'll keep watching the plugs...
pete

When I pulled the plugs after my run in with the dud chinese condensors I was astonished to find they were a light brown on the insulator. Just like a pic out of a 1950s Practical Motorist. This is running on Shell V power. At various times and states of tune they have been white sooty wet etc and even when they were a mess the car still ran well, it just used to hate idling for long periods. This is with the new dizzy, fuel pressure regulator AAA needles etc etc.
Stan Best

This thread was discussed between 03/07/2007 and 09/07/2007

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