I had a serious tank slapper with my 96 Sport right after I bought it. It was my 3rd Guzzi and I knew that shouldn't have happened. I entered a nice high speed sweeper at maybe 80mph but hit a series of three minor bumps in the road and that set it off. The bike recovered after I rolled off the throttle. The previous owner of the bike was 40 pounds heavier than me and had the rear spring preload too tight for my weight. I backed it off and never had that problem again, in spite of riding way too fast for public roads. I don't ride that fast anymore. I still enjoy a spirited ride, but not stupid fast.
Makes me wonder if I am not too light for my Cali. Stiffening the damping of the stock shocks was not much good. When they "died", the replacements had to be set on a hard ride to ease the front-end wobbles in bumpy bends (at speed

) Wasn't a cure. Only new fork springs worked. FWIW, my weight is about 160 pounds and I sit as upright as possible, although now that I think about it, that probably does not apply when cornering fast. Others might want to set me right on that. I am really not sure what posture I assume in bends.