Originally posted by knary
So aside from the springs, you've got the front forks of an '86 K75?
If "yes", there's your answer. By '91, BMW had put the 'S' type forks, as found on K75s's, to the full line of K75's. So though you've got relatively fancy springs up front, you've got the damping of the older forks which were known for their bouncy old-school BMW feel.
Also, when the PO installed the springs, they may not have taken the time to increase the preload. Since you're a ...um... bigger person, the stock preload is probably insufficient.
The best bet, if you want to match or do better than what you had with the old bike without the expense of installing 'S' forks, would be to install some racetech cartridge emulators. They can be, from what I understand, tricky to get set up properly but you probably can't do much better - especially at $150.
race tech cartridge emulators