This is a post by "grizld1" I believe, from a few years ago:
Throttle Shaft Seals
BS38 (70-79) and BS34 (80-83) throttle shafts have a rubber seal at each end. Before attempting to replace the seals, remove the throttle shaft springs and check the shaft for play. If it's wobbly, new seals may work for awhile, but the pivot area in the throttle body is worn. Replacement is cheaper, but motorcyclecarbs.com remanufactures to spec.
Mike's XS lists seals for the BS38 but excludes the BS34 from the application list. For the purposes of this article, I dismantled a BS34 from a 1982 machine. Comparing its seals to a new one sold by Mike's for the BS38 showed no visible differences--same seal type, depth, and diameters. The reason for the exclusion may simply be that for some inscrutable reason the seal was not shown in XS650 parts books from 1980 on, and Mike's has followed that lead.
To remove the throttle shaft for seal replacement, the throttle plate must be removed. If you open a throttle and look at the back of the throttle shaft, you'll notice that the tips of the screws protruding from it are cross-hatched. They've been staked--that is, deformed slightly to prevent them from backing out, entering the intake port, and tearing up more stuff than you even want to think about just now. They're brass, so it's very easy to destroy the head, and removal is usually troublesome.
Your chances are improved by using the right tool and controlling the workpiece. First, note the orientation of the throttle plate, and mark the shaft for its exact position. If you're rebuilding more than one carb, keep the throttle plates paired to them. Set the carb spigot-up in a carefully padded vice, with the slide removed and the back of the throttle shaft supported--a wood or plastic screwdriver handle minus the shaft or a piece of large wooden rod works well. Choose a screwdriver with a precise fit to the screws, give it a light but firm tap to seat it, and use both hands to apply a short, sharp push-and-twist. This will usually break the screw loose. If the screw does not break free, try heating the area with a hair dryer or soldering iron (not a torch or high-temp heat gun!) and quenching with penetrating oil from a spray can. Back it out two-handed, applying downward force as you turn, until the staked brass cleans itself up in the steel threads of the shaft and turns easily. If the screws must be drilled out, bear in mind that a trip to the machine shop will be cheaper than new carburetors.
Member Fry posted an excellent tip on removing the screws. After carefully drilling the screw heads and removing throttle springs and stops so that the plates would rotate fully, he was able to grip the staked tips of the screws with needlenose pliers and back them out. Thanks, Fry!
When you reassemble, use blue Loctite and restake the screws with locking pliers (Visegrips) or waterpump pliers (Channel Locks).
My own comments:
The regular phillips screwdriver tip is too pointed for those screws. Its very important to have the screwdriver tip go fully into the screw recess. I have blunted the tips of my screwdrivers and they will fit much better.
