Blueing or discoloured exhaust headers

[JohnT]

I have inconsistent blueing across the exhaust headers of a 1981 CB750KP, cylinders 3 and 4 are discoloured, whereas 1 and 2 are not.
Where should I start?

Thanks

 

[drgnrdr750]

The blueing is from the pipes getting hot. I would start with making sure that the spark plugs are the same. Then check the carburetor adjustments.