Here is an account of the air box removal on my 85 K100RS to access the fuel pump regulator. I have permanently stripped the plastic to ease maintenance. For this job, I have removed the fuel tank, the seat and the EFI.
Step 1: Remove the airbox snorkel. Remove the two bolts and pull the snorkel out of the box. It is a press fit.
Step 2: Remove the air filter. This is sandwiched between the top and bottom halves of the airbox.
The filter looks like this.
Three clips hold it, two rear and one front.
Here is a shot with the filter removed.
Step 3: Detach the outlet elbow.
There are two clamps. You can use a flat head screwdriver or a 7mm socket. Loosen the rear clamp. Pull the hose off. This will require some force.
Step 4: Remove the air flow sensor. This is screwed to the top half of the air box.
Here are the two screws on the top.
You can now detach the sensor from the air outlet elbow. Careful, the plug and harness is still attached. Turn the sensor over to access the plug.
There is a metal clip holding the plug. Remove it and the plug will pull off.
Step 6 : Separate the plug/harness from the top half of the case. Do this by pushing the grommet the harness runs through out from the inside of the case. The result is this.
Step 7: Remove the bottom half. There are two allen bolts holding it.
Pull the lower half out and you see this.
And there is the fuel pressure regulator.