You reminded me of a High School auto shop thing. I was assigned to do a tune up on a car belonging to one of the women teachers. I did and confirmed that all the settings were correct. Point gap, dwell, timing, idle mixture and idle speed, etc. Road tested car with shop instructor and all seemed well.
The teacher returned about a week later saying that her fuel milage was very low. I went back through my work to see what went wrong. This was, after all, a "come back" and I was still just a student, not a "real" mechanic. I found the plugs lightly fouled with black soot. I cleaned the plugs and carefully disassembled the carb for inspection. Finding nothing wrong, I put everything back together and road tested the car. Pulled a plug for inspection and it was burning correctly. Shop instructor road tested the car and released it to the teacher.
She returned a few days later and said it was no better, perhaps even a little worse. Before going any further, the shop instructor asked if they could go on a road test, with her driving. She said yes. As they got into the car, she pulled the choke handle most of the way out and hung her purse on it.
Maybe you need to be old enough to remember manual chokes to really understand this.
