Have an older wheel? Look here.
Adjusting big wheel spring
The right side crank is attached to the main axle with a setscrew, and captures a spring which controls the pressure between the big wheel and the flyer drive wheel. When the spring is tighter, the flyer drive wheel has better traction, but causes more drag on the big wheel and more treadling effort.
To adjust the spring tension, support the big wheel from the left side, and slightly loosen the right crank arm's set screw. While holding the big wheel, compress the spring with the crank arm until the desired tension is achieved.
Too little pressure will cause the flyer drive wheel to slip, while too much pressure will cause premature wearing of the o-ring and/or cause circles on the big wheel. These marks can be removed with De-Solv-It cleaner, available at hardware and grocery stores.
Adjusting flyer shaft collar
The collar should be positioned just below the upper bearing, to keep the flyer shaft seated in place while spinning. The collar and bearing should have a gap about the thickness of a few pieces of paper, but the actual measurement isn't important -- just that there's a slight bit of wiggle room.
Humidity changes will cause wood movement, which can slightly increase or decrease the curve of the upper leg. This can change the gap between the collar and upper bearing, requiring an adjustment. If the collar pinches against the bearing, treadling may be difficult and/or noisy.
To adjust the collar, loosen the setscrew a 1/4 turn with the smaller hex key. Slide the collar downwards, then reposition with a proper amount of space between it and the bearing. Retighten the setscrew fully.