I hadn't replaced these at the time I'd rebuilt the carbs with new o'rings, jets & needle, seals & gaskets. Forum opinion was there was a large hassle factor in replacing these, & that they were generally fine.
However I thought the carbs might have had an air leak thru' the throttle o'rings. I have been suffering a bog in the first throttle application that I haven't been able to tune out, & I thought I'd better do these for piece of mind if nothing else.
Obviously 1st remove the carbs from the bike. Disassemble the throttle lever mechanism (nut & two piece lever), & The throttle spring base (two scrows into the carb body).
I marked the front on the throttle butterfly (& which side was up) for easier reassembly. The Butterfly has a chamfer on it. Turning the butterfly, you can see where BMW have deformed the screws so that these will not loosen & enter the intake. You need to file this portion of the screws away.
I took the throttle slide off so I had more room to move. I didn't need to take the float bowl off. I had thought the screws might be loctited in & I might need to heat them to release this. This proved not to be the case.
The throttle butterfly shafts slides out once the butterfly screws & butterfly are removed.
Replaced the o'rings, with a bit of vaseline smeared round them to assist reassembly, the rebuttoned everything back together. I used red loctite on the (shortened) butterfly screws, & a small screw driver to deform the small amount of thread showing after reassembly, to ensure that these don't fall out on their own. Jobs done, piece of mind restored.