I reckon a lot of the breakdowns on older cars without engine management were down to the ongoing tinkering that owners indulged in!
How many people have you seen adjusting ignition timing without a strobe? Or turning carb screws 'an extra half turn?' Worn rocker arms set to specified clearances without allowing for the wear?
I'd hazard a guess most enthusiasts could get mixture and timing "good enough" by ear back in the day.
Ah, but that was never good enough! I spent hours adjusting the two screws, checking the timing, but there always was "just another tiny adjustment"!! When you were working on a 10 year old engine on an old banger with worn carburetor parts, it was a never ending job.
I good mate of mine, now sadly lost touch with, used to do "legal" road rallies, and was always adjusting and balancing his Webber 45s' with just his ear to the engine. With a fag on the go at the same time, obviously.
Yes, balancing them and adjusting the mixtures was Ok, but then you needed a whole drawer full of jets and emulsion tubes to change anything else.
Or a full boot, as was the case here
But he was pretty spot on by ear though, which I was always stunned by.
I work with a guy who used to build F1 engines, then had a business remapping and uprating cars. He's another who can do shit by ear, despite usually having an array of sensor feedback to guide. God knows how/why he got into servers. Well, apart from the fact he blew his unit up one day