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Gt6 mk3 plug colour


Danwedges
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My car seems to be running okay so I cleaned my plugs last week to check the colour so after 100 miles this is the colour of them and was wondering should I lean the mixture off? The outer ring is black with carbon but the centre and electrode is virtually uncoloured I've always been told to aim for a tan/brown colour and these plugs are making me think it's rich and lean at the same time? What's your opinion?

Thanks 

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Pleased to see they're including red coating, as in picture 2, this is caused by using fuel additive. I was surprised to find mine had turned pink and moving towards red. I stopped using additive after Uncle Pete told me about the "memory of lead" and my plugs eventually went back to picture 1. 

The plug in the first pictures do look a little red, but running rich. Second set a gnats too lean? 

 

Doug

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I've adjusted 1/4 turn would you recommend another 1/4? Or should I leave as is and check next weekend? I usually do about 100 miles a week and it only ever sees shell v power as anything else seems to run flat and cause overrun. I stopped using fuel additive a few months ago after reading about lead memory so maybe the red colouring will disappear after a few more months 

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I had bother the last time I used the colour tune on mine showing flashing yellow on idle and white at higher revs which I put down to the air filters flowing too much air which was causing a flat spot at 3500 under load but this has been cured with velocity stacks inside the air filters and the top half of the filters taped off to reduce air in but I haven't checked with the colour tune since so probably a good idea I'll have to dig it out of the back of the garage

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Plug colour is only a useful guide if checked after a good hard run (some would say should be done by cutting the engine from cruise and coasting to halt!).

To indicate what is possible with these old engines, when fitted with modern(ish) electronic injection, correctly set-up, the plugs will be almost completely clean and deposit free even after thousands of miles.  The engine in the pic was a fairly heavy oil user too as can be seen from the head deposits.

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10 minutes ago, Danwedges said:

I had bother the last time I used the colour tune on mine showing flashing yellow on idle and white at higher revs which I put down to the air filters flowing too much air which was causing a flat spot at 3500 under load but this has been cured with velocity stacks inside the air filters and the top half of the filters taped off to reduce air in but I haven't checked with the colour tune since so probably a good idea I'll have to dig it out of the back of the garage

The problem with Colourtune is that it was originally intended for fixed jet engines where the idle mix setting was just that and didn't affect running elsewhere.  On Strombergs and SUs the mixture setting affects the whole range and these engines idle best slightly rich, so the needles are factory selected for this.  Therefore, to get the blue colour at idle you end up leaning it off too much and getting poor running/flat spots further up.  MoT emissions adjustment tend to result in the same effect making it necessary to richen things up a bit after the magic paper is issued.

You may get better results with colourtune if you treat the point at which the flame goes blue as a marker point and then richen back up a couple of flats until it just goes orange again.  Blanking off part of the airfilters is an.......um..... unusual approach.  If you have fitted aftermarket "free flow" air filters such as K & N and perhaps have exhaust mods too, you actually need different needles to compensate for the extra gas flow through the engine.

Nick

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The carbs are off my 2500 engine that were running fine but it threw a rod and I replaced it with a 2000mk2 saloon engine and the same setup for this leaned out excessively on the smaller engine which was the exact opposite to what I was expecting but being hif carbs I couldn't try a standard airbox so that was the only way I could think to restrict airflow a bit with what I had in the garage and it actually worked haha

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