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Not exactly what I wanted to see when removing my spark plugs on Saturday. A sliver of ceramic missing from the nose of number 4. Also a distinct colour difference between cyls. 1-2 and 3-4. I've already taken steps to remedy the situation. The purpose of taking out these NGKs was to fit Champion N9YCs.

The siamesed port system, leads to something called “charge robbing”, for each siamesed pair, the first inlet valve to open starts the air/fuel mix off in that direction and even as the valve closes the momentum of the air continues in that direction, so the second valve gets robbed of part of its charge. This means that cylinder 2 gets more fuel/air than cylinder 1 and cylinder 4 gets more fuel/air than cylinder 3.

This means that if you say ColorTune on cylinder 1 and get that mixture correct, then cylinder 2 will run rich, or if you ColorTune on cylinder 2 then cylinder 1 will run lean. That’s why you have two sooty spark plugs and two grey/brown spark plugs.

It’s a basic engineering compromise of the the siamesed port design and affects all A and B series engines.

I’d never use Champion plugs.
After working for a supplier many years back that sold literally millions of spark plugs it’s one make I won’t use. Far more problems than the NGK or Nippon Denso equivalents.

What was your planned remedy???

I’m with David on spark plug choice, NKG plugs have a much lower failure rate than ALL the well known European and US brands.

I would weaken off the back carb slightly 1 to 1 1/2 flats give it a run and recheck. My plug choice would be NGK or Bosch. Not used Campion in a long time as used to have high failure rate.
Dave

Haven't seen champion plugs around for quite some time, motor factors always seem to have NGK instead, they've always been Ok.
Big question is bpr 5es or bpr 6es? I think bpr5 is the equivalent to Champion N9Y. I assume the 6 is hotter?
I tried a colourtune to set the mixture but went back to using the carb lifting pin/engine note method on the as per Haynes manual.

Really? Oh hell. Last year my ex motor trade neighbour was telling me to get Champions over NGK for much the same reason. When I asked why all I could get was NGKs at places like Halfords and the local motor factors, he reckoned it was a monopoly type thing where NGK were paying bonuses for people to stock their plugs. I've still got a nearly new set of NGKs bought and fitted just before my neighbour told me all of the above. The sooty and overheated ones were the originals when I got the car, refitted in desperation when I couldn't get it started in May. The nose of one wasn't chipped then though. That could have occurred either when I went for a blast last week, testing the car for cooling efficiency in hot weather, or during the difficult starting period after winter.

I've already re-balanced and re-tuned my carbs Dave. That job I couldn't do for love nor money previously. I found it dead easy now there isn't a blocked exhaust or manifold leak. AND in spite of the good work Glyn at the local garage did for me last year, and knowing twin carbs can go out of balance and tune easily, I think they still weren't properly set before. I've got one of those German made 'snail' balancing tools, and the carbs weren't pulling the same amount of air, and I weakened the mixture on the front carb by two flats, and richened the rear one by two flats, using my Gunson Colortune in cylinders 1 & 4. And I checked and re-checked my adjustments several times before settling on what I had, just taking the mixture slightly off rich to give a blue flame, as per the instructions. I just cannot handle that piston lifting pin business, raising it 1/32" on a hot shaking engine. I was happy using the Colortune. Now the car seems smoother on idle than it has ever been, and doesn't feel like it is going to stall after a minute or so of being held in Drive, on the footbrake, when the transmission drags the 900rpm tickover down to around 500rpm. The car seemed to run better on choke too. I'm just a bit concerned about what happened to that sliver of ceramic from plug number four. No surprise in that I couldn't see any foreign bodies when I shone a Mag Lite in the cylinder and turned the engine over by hand. I hope it just blew out of the exhaust port. I can't notice any potential damage when the engine is running.

MarinaCoupe wrote: ↑Tue Jul 17, 2018 9:40 pm The siamesed port system, leads to something called “charge robbing”, for each siamesed pair, the first inlet valve to open starts the air/fuel mix off in that direction and even as the valve closes the momentum of the air continues in that direction, so the second valve gets robbed of part of its charge. This means that cylinder 2 gets more fuel/air than cylinder 1 and cylinder 4 gets more fuel/air than cylinder 3.

This means that if you say ColorTune on cylinder 1 and get that mixture correct, then cylinder 2 will run rich, or if you ColorTune on cylinder 2 then cylinder 1 will run lean. That’s why you have two sooty spark plugs and two grey/brown spark plugs.

It’s a basic engineering compromise of the the siamesed port design and affects all A and B series engines.

The sooty plugs are from 1&2 and the pale ones from 3&4 Chris.

A chip like that is most likely to have been caused when the plugs were fitted or removed, it looked like a “percussion” chip, where the ceramic nose has been caught creating a weak spot. Then the heat/cold cycle has opened it up until the chip came off.

mickthefitter wrote: ↑Tue Jul 17, 2018 11:07 pm

MarinaCoupe wrote: ↑Tue Jul 17, 2018 9:40 pm The siamesed port system, leads to something called “charge robbing”, for each siamesed pair, the first inlet valve to open starts the air/fuel mix off in that direction and even as the valve closes the momentum of the air continues in that direction, so the second valve gets robbed of part of its charge. This means that cylinder 2 gets more fuel/air than cylinder 1 and cylinder 4 gets more fuel/air than cylinder 3.

This means that if you say ColorTune on cylinder 1 and get that mixture correct, then cylinder 2 will run rich, or if you ColorTune on cylinder 2 then cylinder 1 will run lean. That’s why you have two sooty spark plugs and two grey/brown spark plugs.

It’s a basic engineering compromise of the the siamesed port design and affects all A and B series engines.

The sooty plugs are from 1&2 and the pale ones from 3&4 Chris.

That’s a mixture problem then, the front carb was running richer than the back carb.

balmy wrote: ↑Tue Jul 17, 2018 9:45 pm I’d never use Champion plugs.
After working for a supplier many years back that sold literally millions of spark plugs it’s one make I won’t use. Far more problems than the NGK or Nippon Denso equivalents.

What was your planned remedy???

I bit the bullet and had a go at balancing and tuning the twin carbs, even though I've been terrified of touching anything since the car was set for me last year. But the lean looking mixture and chipped plug nose from cylinder 4 (the photo of four plugs shows those from cylinders 3&4 on the left) meant I had no choice really. I believe I found the job easy with no other faults in the system like I had when I bought the car. Although I note Chris's description of the siamesed ports. Still, hopefully what I perceived as a happier and smoother running engine after my work, is a good sign. I planned on having another look at the plugs in a bit and seeing as there's an overwhelming lack of support for Champion plugs, could be I put back my newest NGKs. It seems people always have their favourites though and my neighbour last year was scathing about NGK plugs and full of praise for Champion!

I think most spark plugs are quite good these days and I am sure that some don't suit some cars but I have never had a problem running the
TC on CHAMPION plugs. When I first had the car I bought it from a FORD dealers who had serviced it and fitted it with F O M O C O plugs
and they didn't suit it at all.

It is a mixture problem one carb rich and other slightly weak. OE Unipart plugs were Champion see very little of Champion at all nowadays
Dave

I use Champion plugs in my 70's motorcycles.
It's what they came with, but most bikes I work on have had NGK's fitted for the same reason - everyone stocks them.
One thing I noticed between the two is that for the same grade of plug - in my case B8ES v N3C - the position of the electrode on the Champion places the spark a little further into the combustion chamber.
I think that is beneficial, especially in the Trident/Rocket 3 engines where the spark plug barely makes it through the alloy head.
Imagine the same might apply to a B series head..

I mean to check on the combustion colour of my plugs before much longer, to make sure my carburettor adjustments look okay, but I think this debate about brands has left me thinking with the low mileage I'm likely to cover in my Marina, it is unlikely that I will experience plug failure with any brand I use, so I might as well stick with the newest Champion plugs for now. I really don't know where my neighbour got his information from about NGK basically paying stockists to sell their plugs over other brands, but he's the same age as me and I've known him for 25 years, and until two or three years ago, when he decided to semi-retire (lucky beggar) for all that time he operated a Snap-On tools franchise with a big Merc van, and he knows pretty much all the car workshops and garages for miles around.