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a set of progressive fork springs and some 10wt will transform your frontend.
+1 on the heavier fork oil, but going to a straight rate spring appropriate for your weight and riding style gets rid of that bouncy suspension stuff. I really loathe progressive rate springs.
The older Airhead forks have a lot of dive in them. After '87 or '88 BMW used the K-bike forks which don't dive nearly as much.
IMHO, the way to set up these forks is in three parts:
1) Get some new BMW HD springs, or Progressive springs.
2) Set the preload with a spacer to archive a static sag of about 25% to 35% of total travel. Suspension has to be able to absorb bumps (unused travel) and also drop to follow dips in the road (sag). Be sure you also set the sag on the rear shock to match.
3) Start with the stock 7.5wt fork oil of the correct amount, and then experiment. Add more oil to reduce dive on *hard* or *quick* stops (in 10cc increments up to a max of 50ccs). Use a heavier oil to firm up the fork dampening over the range of normal travel (normal bumps in the road).
This last part will take some time, but it's amazing just how good your forks will work many times after some trial and error with oil weight and amount.
I agree with all of this and the K75 I picked up in May went through most of the process, however, what you're doing in this process is compensating for the progressive rate spring coil. Progressive rate springs are still terribly bouncy and the front end dives too much before getting to the part of the spring stiffness curve that is appropriate. Progressive rate is old technology.
I went to 1.0Kg/mm straight rate springs on my Vstrom and that's the way I want the K75 to feel -- a good solid front end without any of that goosey handling or brake dive. I'm sending one of my old OEM BMW springs to Sonic Springs in Oklahoma so he can match it up size-wise with a straight rate replacement.