First, please do not use the right extruder and please print flex filament without guiding tube.
Usually we suggest lower temperature instead of higher. Since you have tried 230, 235, 240 both not ok. I suggest try some lower temperature. Or you can share the pictures of melt tip of your filament here every time when you find air printing at different temperature.
distance mention by Billucas is also a good point. When loading filament, try manually drag the filament. If it can be drag out from the gear
very easily. That means the distance between feeding gear
and bearing is too far.
You can loose the motor fixing screws and insert some shim into the left side of extruder motor to move
closer to the bearing. Like the following picture.
Here is something modified by Michael:
To ensure tight connection between the feed gear & filament. Place 0.62mm x 12.7mm wide heat resistant shim between the left and right sides of the respective E0 (left) & E1 (right) stepper and the tall vertical filament extruder housing. Unload the filament, remove the clear cover, and then the 4 recessed socket head screws on the front side using 2.5mm hex key. This will slightly angle the feed gear closer to the v grooved bearing.
To make my shims, I used 4 layers of 0.155mm X 12.7mm nylon tape label from my Brady BMP-21 labeler.
During testing of the RIGHT(top) extruder, I could get a stronger grip on the filament with out the shim by unloading the filament, removing the clear filament feed cover, loosening the 4 metric socket heads, sliding the stepper as far as possible to the right as viewed from the front. While holding that position retighten those 4 bolts on the right extruder.