Try our new info resource - "Aladdin's Cave" (Main menu)Just added a separate link to Ash's Dropbox thread (shortcut)
Thinking about this Erny over a few days, did you see a previous thread on here with very similar problem (I forget which owner) and it was a problem none of the suggestions we made got the problem.Finally turned out to be the original exhaust of one cylinder was partially blocked within the first section. It seems it was manufactured with the pipe's inner skin deformed about 200mm down into the pipe from front entry. If you removed the pipe from cylinder two and either put a camera down there or something to see if there's a restriction it would tell you.
I've tried searching for it but so far can't find the thread, someone else may help remembering to give us a link.Pictures of it posted and cut open afterwards as pipe was scrapped.
Graham, thanks for your opinion, I start to feel the same now I managed to have another coil (from 550F 1976) to test - result is no change, plug 2 still darker than others.Next:waiting for intake manifold to replace mine w/o grooves. Carbs will go off again, so time to re-check around air screw (did not checked before).if no improvement, I'll try to look at another carb set