Evan is spot on. I would suggest finding a low air setting by removing the exhaust pipe and using your hand to feel the air pressure. Are you getting some air flow at 1? Whatever the low point is I'd increase it a bit, say if low is 1; use 2. And leave it there for the entire roast until first crack begins. Looks like you have a window to see the exhaust, increase the air just enough so the smoke is coming out nicely from the pipe. The idea being your running the roast using the gas knob until you get some solid results, and then add in more air adjustments.
Another thing you can play with is to set the gas and air on a medium setting and idle the machine at a fixed temperature (without beans). What happens when you increase the gas, or the air? All of that changes with green coffee in the drum, but it doesn't hurt to get a feel how it operates. At least you can find a warm-up setting where the time corresponds with your preferred charge settings.