In my humble opinion, if you're really worried about meeting emission
requirements, SU carburettors are no option. I've tried a number of ways to
adjust mixture when I still had the standard 4 cylinder car with twin HS4
carbs, including the color tune glass spark plug. I found that it ran too
lean (like you describe your car) when I got the colour of the flame in the
blue. I finally settled on the "lift the piston" method as fairly reliable -
good performance when hot, the right colour brown on the plugs when we still
had the lead in the gas (I understand from other sources that with modern
lead substitutes in the gas, the colour of plug deposits means very little).
In my country, the emission requirements for the year of manufacture apply
to classic cars. For my '68 car, there are no requirements! But if there
where, I would have the mixture set for emissions on the MOT and directly
afterwards reset it for performance myself. It doesn't hurt to re-adjust
once a year anyway. Modifying manifold/carbs sounds like quite an investment
to please the rule makers!
Regards
Frank van Dalen
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administrator. mjb.]
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