Im currently still in the process of tuning my engine and decided to pull the spark plugs out to have a look at how they are running. This is what I found. Seems like the outer cylinders and running lean.
Any ideas?

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If its yours, customize it !

It is hard to read plugs properly now the tetraethyl lead has gone out of the fuel.
I'd say the inners are rich rather than the outers being lean, unless those electrodes are blistered too.

BTW, this week all 4 of mine look exactly the same with a Dellorto 45 carby on, they are light grey.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Yes I agree with the Doc number 2-3 cylinder look rich rather than 1-4 being lean not unless you want it running really rich.

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Present
- 1968 Morris Mini Deluxe- resto
-1979 Leyland Moke
-2007 R56 MINI Cooper
Past
-1964 Morris Mini Van
-1965 Morris Mini Van
-1961 Morris Mini 850

its pretty typical for a single SU car/manifold system to run like that

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

You can expect the two inner cylinders to be a bit richer than the outer, simply due to the siamese inlets. The fuel needs to travel further to the outer cylinders.

If they were my spark plugs, I'd say that's a good result for tuning. I'd rather have my inner cylinders a little rich than the outers lean.

Right. So I'm best of not leaning it off too much then?

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If its yours, customize it !

According to Vizard? (I'm pretty sure it was him) when running a single SU you can reduce this mixture variation by grinding a radius into the outer faces of the intake manifold just before the gasket face, biasing flow more towards cylinders 2 & 3.....

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I note you're running BP7ES - thats a colder than normal plug. Engine has had a bit of work done to it?