And not just unleaded gas. Between the quality of the gasoline until the 1960s and the cleanliness of the combustion process, pulling the head to scrape carbon off the piston tops and combustion area was a common practice at one time. Your average competent do-it-yourself car owner would do it as often as needed.
There are a couple of books by a guy who bought a WWII surplus amphibious Jeep and modified it to be ocean-worthy so he could sail/drive it around the world. In the middle of the first one, he describes pulling the head off the Jeep motor mid-ocean (not easy, because there was a cross-member just above the motor) so he could scrape the carbon off the motor, and realizing, while the head's off, that there's a huge storm brewing. He manages to finish the job before the storm hits, so he can turn the Jeep into the waves.
I own one of these; never found a use for it, but I'm sure there's a use lurking out there somewhere.
