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MG Midget and Sprite Technical - Plugs (brown grey, any advice to improve?)

I have the Champion colour chart and have just looked at my plugs to see how we are doing. For 'normal' the chart says grey brown deposit. Mine are all the same and more brown grey. Definately not oily. Definately not black sooty (they were before I had a go at the carbs). So just wondered if anyone had any advice to get to the all conquering 'best' colour.
At the moment I have NGK 7822 BPR6ES on the advice of this site (was it you Guy?) from last year when I got it back together on its wheels and they do work fine. The exhaust smells rich (not full of petrol) especially on starting but gets better once warmed up. The car starts well, pulls well, changes down etc. all with good engine noise. Any thoughts for improvement to the all conquering grey brown?
Dave Squire (1500)

Dave

I believe most of these charts were made when we still had lead in petrol, I'm not convinced you'll get the same grey brown colour with modern fuels. Do you use a fuel additive? as I believe these change the colour of the plugs. If it's running well I wouldn't worry about it, you are after all talking about an engine that's 35 years old and they didn't run that brilliantly when they were new.

Bob
R.A Davis

I would agree with Bob. You could end up making it worse if you start tinkering. Everybody wants to own the perfect car, but I think if we did we would start looking for faults or things that could be made better. That's just our nature I guess.

Andy
Andy Burrows

Fuel mixture
This is the most important part of plug reading and the most misunderstood. Mechanics are often talk about "color" on their plugs. However there is only one color to look for on a plug and that is black. It is soot, the remains of combustion.

The brown color you see on a plug is only the result of gasoline additives and nothing more. In an engine which is running well, the plug will run hot enough to burn off all the brown color, leaving only white and black.
Lawrence Slater

So Lawrence, do you reckon a hotter plug will help?

I've got the oil leaks to fix first this weekend so not rushing to change the plugs at the moment. I was looking at changing them soon ish though (hence the thread) as they may only have done 750 or so miles but they are the ones I put in first after freeing the engine up so they have had some relative abuse with the old engine oil to begin with, then I had to learn to do the carbs, then the throttle cable was not relaxing so had high rev tickovers in town traffic .... etc.

Or would you stick with the existing and go back to the carb setups, clearance, and timing?
Dave Squire (1500)

Your plugs sound fine to me, so I'm with Andy and Bob on this. 750 miles is nothing for a set of plugs and they'll stand the minor abuse you've described and other than re-gapping and cleaning them (which I doubt is necessary from your description), I would say leave well alone and don't do any further tinkering with carb setups, clearance and timing.

Irrespective of the variable colour reproduction, I have never got a match with the Champion colour charts except for the black, wet and oily ones! And that's in over 50 years of tinkering with A series engines....
Peter B

clean 'em check the gap put them back in and drive the car more

when you do your next service you'll be checking and possibly adjusting items - to mess around unnecessarily in the meantime will end in fiddling with carbs, there's a difference between necessary adjustment and unnecessary fiddling, the necessity

howd' ya know if the chart's faded(?)
Nigel Atkins

Hi Dave
FYI My 1500 runs almost pure white using 96 octane with a fuel additive. On 91 Octane I get some black and she runs on, definitely not good. I have notes and repair dockets from the PO in England saying that they thought that the problem was the fuel. Gee Whiz they were correct. Next step I'll try the 98 and see what happens. Will definitely advance the timing though.
cheers
Rod
R W Bowers

Quite often the colour just informs you whether you are running the right grade of plug not whether the fuel mixture is correct. If you run a colder plug eg BP7es it may well be blacker as the plug is not at temperature, if you run a BP5ES you might get a whiter plug as it will be hotter, maybe a little too hot. Grey on plugs is a lead oxide when lead was in fuels. Brown tends to be a manganese when folk are running some of the octane boosters. If we add toluene we always get a black sooty tinge even when all is just right. To test fuelling at different throttle openings you can do a plug chop. Switch the engine off at whatever rpm/throttle opening. Pull the plugs and check the colour. This assumes you are running the appropriate plug. Works well with two strokes.


Peter
Peter Burgess Tuning

Thats great guys, I get it. No additives or anything so the colour is just for ordinary unleaded.

I will try some V power or Ultimate next fill and see what happens to the plugs then.

If things stay the same I will get some BP5ES's for a try and see if it makes any difference.
Dave Squire (1500)

as a preference I run Tesco Momentum (99), second choice Shell V-Power, third choice BP Ultimate or other 97

what makes you think your engine is off standard and needs the 5s
Nigel Atkins

This thread was discussed between 09/04/2013 and 10/04/2013

MG Midget and Sprite Technical index

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