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MG TD TF 1500 - Reading TF sparkplugs

Afternoon all.
How many T Type owners have perfect looking sparkplugs?
I have been trying to fine tune the mixture using both the condition of the plugs and colortune. According to colortune and rpm reaction to the piston lifters the mixture is correct, but at the same time visible black "soot" on the electrodes and core noses indicates the engine is running rich. Weakening the mixture slightly reduced the sooty deposit, but caused a black, shiny coating to build up on the electrodes, indicating too weak a mixture. The core noses became coated with a darkish brown deposit. A weak mixture was confirmed by a tendency to run on when the ignition was turned off and the engine was hot, after idling at 800rpm. I'm using Castrol Valvemaster in 95 octane petrol and wonder whether the additive is partly to blame for the black glaze. I have driven a fast seven mile test route after each adjustment - is this too short to clean off the plugs?
John
John James

John

All my life I have been unable to get to grips with that dratted perfect advice from Philip Smith, perfect gentleman engineer, to carefully lift each damper with a cycle spoke for one eighth of an inch and see if the engine note rises or falls. And then do the same for the other carburretor.

I have always gone on the spark plug colour and the best pictures on the web I think are the ones highlighted in a recent thread - http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

I always go for light/mid brown/grey in the middle and darker on the rim and that plugs 1 and 4 look the same. I also find that 98 LRP produces a better burn than standard unleaded petrol.

And getting a smooth tickover at 800rpm really depends on what kind of cam you have installed ...

Regards

David
David Wardell

Thanks David
What a useful reference. I would describe my 1&4 plugs as 8 or 9 with a tinge of gloss on the electrode. I really need to go on a long run to confirm their health. Since I fitted pertronix electronic ignition the factory cammed engine will tick over smoothly at 500 rpm. I increased it to 800 to generate some amps and allow for the rpm drop when the clutch is pressed in.
All the best
John TF5924
John James

Modern fuels and additives makes plug reading difficult at best. T-series cars tend to run rich naturally, with slightly sooty plugs (just my opinion from a couple in the area). I think "running on" is more a function of carbon build-up than mixture. I watched John Twist adjust carbs on several cars at a recent GOF- he uses the exact method described by David above!
George Butz

George
Just one flat richer will cure the run on. I haven't tried advancing the ignition a bit to stop it as I don't want to disturb a good proven set-up. Other run-on causes are, Fuel grade too low and tickover too high. I'm sure carbon is not a factor here as the engine has only done 17500 miles. I find the piston lifters tricky as the seem to give varying results. That's why I'm using plug condition to make final adjustments.
John
John James

Hi Guys, since the lead was removed from the fuel we really can't use the old method of reading the plugs. The lead used to cause the white deposits and burn the plugs. Now we get black soot and the plugs last for years. Check the colour of the exhaust for a demo of this. Now it is also black soot instead of light grey. Same deal. The carbies will have to be tuned using the piston lift method.

Cheers,

Paul.
Paul van Gool

Paul

I suppose it might depend on how the engine was converted to run on unleaded. I vaguely recall some wonder simple additive that could be attached to the engine that automatically made unleaded petrol leaded again. In that case the spark plugs would look a beautiful brown colour.

In any case, mine certainly do!

There is another spark plug site at

http://www.sparkplug.co.uk/

which gives lots of technical info, translations of spark plug codes for NGK and Champion and a cross referencing system for plugs from different manufacturers. And more pictures for fault analysis from plug appearance.

Regards

David
David Wardell

David
I buy my plugs from sparkplug.co.uk. Which type do you use? With both NGK BP6ES and Champion N5C plugs I can only get the ceramic nose core to go brown. The top side of the electrodes always finish up with a thin coating of shiny black soot on all four plugs. My unmodified engine is not burning oil. Compression on all four cylinders is a textbook 150-152 psi. I use Castrol Valvemaster with 95 octane which might account for the black coatings.
John
John James

John

I was using N7YC but changed to BP7ES and got much smoother engine running. However they do seem to behave better with 4 star LRP than Unleaded. I get a result which looks something like pics 13 - 20 in the site I posted.

I presume it also really depends on what kind of driving you do. I seem to spend my time finding all the country lanes in rural Buckinghamshire and stay off the dual carriageways so the engine never gets the heat of sustained high cruising speeds. I keep wondering therefore if it could stand a hotter plug (ie for a cooler engine - always confuses me!) but I figure, if the plug colour looks OK, why change? Then again, have I considered the effects of air temperature, humidity and pressure ... ?

I don't use any additive in the petrol.

Regards

David
David Wardell

David
Very interesting, as I keep to similar types of roads. I have been using hotter plugs than you (N5C & BP6ES) which ought to give cleaner results assuming everything else is set up OK.
(the carbs are as lean as they can go without causing weak mixture symptoms. I too find the NGK plugs give slightly smoother running. I printed your colour reference on photo paper and after close comparison reckon my BP6ES's look most like picture 10 or 14, but with a dry, glossy black layer along the top edge of the electrodes. I think the Valvemaster additive might be the cause of this so I am going to email Castrol for advice.
Regards
John
John James

John,

One must realize that the Brits amd US have very different petrol (gasoline) No-Lead formulations.
Here in the US, it is even different from area to area to meet different environmental conditions.
We also don't have the Castrol additive available here.
Thus, we seem to find different results in US vrs UK.

I have found the old "color" standard are no longer applicable, and you tend to get some black no matter how you are tuned. (Even with the "NOLEAD" additive available here)

The only thing I am sure of is that all the US formulations burn hotter and the fuel is less viscous, resulting in faster flow at any given setting (runs richer).

I hope we can develop a modern "plug color" for today's conditions.
Don Harmer

This thread was discussed between 10/06/2004 and 15/06/2004

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