Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG Midget and Sprite Technical - plug colour

Confession time! I've not touched the mixture, timing or pretty much anything else in the engine department for a good couple of years as all seems to be running well and if it ain't broke......
However as I was changing the oil at the weekend, I thought I'd whip the plugs out and have a look and they're all a bit sooty. My feeler gauge seems to have been eaten by the garage monster so I couldn't check the plug gaps but they look somewhat wider than the .025-.030 I believe they should be. Could too large a plug gap be creating insufficient combustion or am I just running rich? I'll try and track down my feeler gauge and have a proper check but think I'll pick up some new plugs in any case. What gap is generally recommended? GKN 6BPES plugs and pertronix leccy ignition.
My HT leads look a bit manky too so I'm going to have a bash at making up my own and then running through the complete ignition and fuelling system to check all's well. Sods law says what appears to be running well now, won't be by the time I'm finished!

I gap my 6BPES @ .025 but I am running points and a Lucas SA12 sports coil. All seems fine.

The sootiness(!) may be because its been idling? I tend to look at mine after a decent blast then switch off coast to a stop and then check the plug colour.

If they are solid copper HT leads unless they are cracked then they should be ok. A good clean round the dizzy and coil is also a good idea.

Bob Beaumont

I would go 32 thou with modern rubbish ethanol bloated fuel.

Peter Burgess Tuning

Interesting Peter, I try and avoid ethanol laced fuel hence keeping the plug gap standard but I guess it all has some in it now
Bob Beaumont

It could be the outside temp... cold weather makes fuel more dense thus more rich...

Prop and the Blackhole Midget

Cold weather also makes the air more dense so more mass of oxygen is breathed in.
M J Chapman

Bob I beleive BP superunleaded doesn't contain any ethanol. I tend to use it as it won't destroy the rubber fuel lines or attack any brass or alloys it comes into contact with.
Jeremy Tickle

Thanks Jeremy. I tend to use shell superunleaded as there is a cheap petrol station just nearby. It looks like its OK. Didn't know about BP though so another option!
Bob Beaumont

Been right through the ignition, new Distributor cap, rotor, ignition leads, adjusted tappets, re-timed the ignition and "tuned" the carbs.
just been out for a blast and revving more freely than before but I think I have a slight misfire at high revs. Testing was limited by the fact that my rear mount for the exhaust sheared and I had to jury rig a get me home solution. Nevertheless I whipped out the plugs straight after switch off with no idling period. No 1 looks a perfect cafe au lait colour, 2 and 3 are still somewhat sooty whilst number 4 is about half way between the two.
I'm not entirely convinced my mixture is perfect but I'm certainly running less rich than before.
Any suggestions? BTW I'm still running on my old plugs. I thought I'd get everything set up nicely before I put new plugs in.

get it on a rolling road.
Do it right, do it once!
David Smith


What carbs are you running?
David Billington

Standard hs2s.
I've thought about a rolling road session. Might be a worthy investment.

Thoroughly clean out the carbs, especially the jets, before re-setting the mix. Check for any leaks or splits in air/vac hoses. Check carbs are suitably balanced. Clean or replace air filter.
M Ogden

Hope to see you at the Ace cafe soon.

G Lazarus

Will hopefully make it in April. I was going to come this month but work got in the way again. Now to go out and reattach the exhaust!

Bill and some of the Midlanders should be popping down too
G Lazarus

April 12th it is then!

'tis true!

two of us (so far)

See you then chaps
Bill sdgpM

This thread was discussed between 29/02/2016 and 21/03/2016

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.