It's commonly know that if you run a petrol engine in (say) a garage with the door closed, you will die of CO poisoning,
Not if it's a car engine produced in the last three decades or so!
At least, not if it has a catalytic convertor working as per its design. It converts CO to CO2 (and to a lesser extent, excess HC to CO2 as well), that's exactly why it's there!
The last MOT emissions result I got, for my year 2000 petrol car gave CO = 0.00 % vol, HC = 5 ppm at fast idle and CO 0.01% vol. at natural idle. I think you'd be alive in the garage for quite some time at that rate. Other methods of doing yourself in are far more efficient!
I certainly agree that modern petrol fuels emit more soot than the old leaded stuff; I have been building and tuning my own engines for over 40 years; I began when performance cars needed 4 and 5 star petrol.
I re-jetted a carburettor equipped motorcycle only last week after making some induction improvements. it now runs far better than standard. A couple of years ago I tuned the mixture on my SU carb equipped modified car after a rebuild (this involved hand modifying mixture needles). To confirm everything was all OK I took it for a rolling road session before we did a long distance touring expedition. The operator was very impressed that according to his highly sophisticated Lambda machine I'd managed to get it stoichimetric by eye, using the spark plug colours. He suggested I richened it up very slightly to improve the power output.