I used to "read" the spark plugs in my street car motors after changing camshafts and or intake, carburetor, ignition upgrades, etc. If the plugs were showing a blackish sooty color I knew I needed to make some changes. That or not cruise, idle around so much and run the car harder. That was sometimes hard to do and stay within the expectations of the local law enforcement personnel. So it was a delicate balance trying to have a motor that would really "get it" when you wanted to play and having something you could cruise around town and not get loaded up and buck, snort and run crappy. Now a days a computer keeps everything tuned just so for all possible driving situations. Way back when, I was seemingly under the hood on a regular basis changing jets in the Holley or metering rods in the Carter carbs and adjusting the timing. I had to wire the coil to a toggle switch because when I had the timing advanced so the motor ran the best on AV gas it was hard to start when hot. I would get the motor cranking over and then flip the switch to energize the coil. I often would go to our local airport on Saturday morning and get a tank of AV gas then go home and crank the timing up so I could "play" that night when all the local car guys had thier toys out. Wow, going down memory lane here.