I never had any problem with the exhaust emissions from my 1974 Triumph Toledo 1300 "HL" and never adjusted the mixture settings!
Just for interest, I always had the MOT inspectors check the exhaust emissions for carbon monoxide and hydrocarbons, which remained within the manufacturer's specifications, up to its final mileage of 101,000, when I laid it up in mid-1999.
Nigel A. Skeet
Independent tutor of mathematics, physics, technology & engineering, for secondary, tertiary, further & higher education.
Upgraded 1974 Triumph Toledo 1300 (Toledo / Dolomite HL / Sprint hybrid)
Onetime member + magazine editor & technical editor of Volkswagen Type 2 Owners' Club