Solex balance question.

[FreeLSD]

Hello.
Recently I've tried to balance dual Solex ADDHE 40 on my Alfa 75. Balance tool reported mass air flow of
7 8,5 7 7 kg/h in 1,2,3,4 cyl accordingly. Unscrewing air bypass 3.5 turns in cyl no.1 have raised it's air flow to 8.5 kg/h , but caused engine caugh at idle and progression. Looks like it's over-leaned mixture in cylinder one, despite air mixture screw was 3.5 turns out.
What was wrong with my actions?

[FreeLSD]

I will answer to myself. Even with 3.5 turns of mixture screw out, A/F mixture was too lean. I saw it with colortune-type transparent spark plug - spark striking alone, with no flame at all. Richening the mixture did the job - even idle with no engine dance.

But there's still unpleasant coughs in exhaust on throttles-closed engine deceleration. Why does that happen?