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MG Midget and Sprite Technical - Unusual plug colour??

Just pulled the plugs to check them - the insulators are brown and everything else a bit sooty but the very tips of the central electrodes are all white - I mean WHITE! What does this mean?

David Banks

To lean.
Arie de Best

With unleaded, I find sooty ring around the body, and slightly off-white electrode (in the Focus and the midget with Kseries).

A
Anthony Cutler

I agree--too lean. I have the same issue after adding Moss K&N chrome filters for stock SU 1-1/4" carbs (even at 5,000 ft), though I only have a little whiteness.

I'm going to put in rich needles this weekend, if dialing down the jets 1~2 flats doesn't do the trick. If the rich needles are too rich, then I'll resort to needle-polishing with standard needles. Here's an article: http://terryhunt.co.uk/mini/pics/tech/picsb/pics.htm

Best of luck - JMY.
JM Young

I agree with probably too lean, but note that this assumes the plugs are the right heat range. Heat range requiremnts will change if you have modified the engine, particularly compressionr ratio (on our fuel at least!).

Plugs which are a little too high can give similar symptoms to too lean, plugs which are way too high have blistered electrodes.

I note though that the insulators are brown - is this on unleaded? If so, note Anthony's comments re appearance.

The middle stages of too high in neat range can also leave the insulator with a brown appearnce.

There are browns and browns - any chance of a pic?

Paul Walbran

Are you running any fuel additives? They can have an effect on the colour, making it difficult to tell what the mixture is doing.
I used to run with Millers CVL and it turned the plugs a strange shade of brown.
Dave O'Neill 2

No fuel additives - just premium pump fuel.

Plugs are NGK BP6ES

No pic as I have since swapped the carb back to the HIF44 SU instead of the Weber 45 DCOE and the plugs are now a much healthier colour.

So I guess that rules out anything other than mixture.

Which means that as I suspected I have a problem with the 45 DCOE - its got a 160 main jet so it shouldn't be running lean should it?

Aux Venturi 5
Choke 34
Main jet 160
Air correction 170
Emulsion tube F16
Pump jet 50
Idle jet 45F9

Anyone know anyone who can overhaul Webers??? I am at my wits end with this carb!!
David Banks

You really need to get on a rolling road to get it properly set up.
Dave O'Neill 2

David

I would expect BP6ES to be a bit on the warm side as far as plugs go if you have raised the compression ratio and are running a road camshaft & LCB. For such engines I usually start with BP7ES, one even had to go to BP8ES.

One way you can detect if the plugs are marginally too hot is to find a long steep-ish hill and drive the car up it at full throttle. If the plugs are too high in heat range the car will run OK initially, but after a while it will start to misfire a bit, and maybe get progressively get worse.

Paul Walbran

kind of off topic but i have a stupid question, should i use regular unleaded gas in my stock 1275?
Seth Brecklin

Depends on the octane rating - do you know what it is?
Paul Walbran

David

If you look further down the list of threads you will see an almost identical one from me! I have moved to a richer needle and that seems to have sorted things (as far as I can tell from plug colour). It's interesting to have two threads so similar!

Chris
Chris H (1970 Midget 1275)

Thanks everyone.

Rolling road isnt really an option. The nearest I know of that can sort a Weber (or an SU) is over 4 hours away!!

I have sorted the HIF44 by running from 2000 rpm to 6000 rpm on a dead straight road and timing the runs and checking the plug colour at the end. Not very scientific or accurate but good enough to get it running REALLY well! (Started on a BDL and ended up on a selectively polished BCE - ruined 2 in the process!)

I cant do that with the Weber though - parts are so expensive and even if I bought a selection most would be no longer required once it is sorted.

My intention has always been to get the Weber reasonably sorted then make the long trek to the rolling road to get both carb set ups finely tuned (and compare them back to back).

I am sure there is a fault with the Weber - it used to run great! I have stripped and inspected it several times and cannot find the problem. There is clearly an issue as it used to run very well - now the plugs central electrode is snow white and its way down on power compared to the SU and its own previous performance and pops, bangs, farts and spits at anything over 2500 rpm. I must be missing something but dont know what.

I think it needs a professional/experienced eye over it - any suggestions? The only place I have found charges £200 fixed fee - I can buy a new one for not much more!

David Banks

Wide Band O2 meter..
Wired up while driving (ideally with a throttle position sensor and Rev counter input.)

Plug reading and colortune seem to be pretty blunt tools compared

Also worth joining the Sidedraft central group on Yahoo if you are going back to the DCOE. Kieth who runs the group is a genius (helped me set up my twin DHLAs on my Lotus Elan)

Tim

PS if you were closer I would lend you my WBO2!
T Dafforn

This thread was discussed between 08/05/2010 and 10/05/2010

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