Those are "O" rings for Keihin carbs and they must be replaced. Those deform with age and dry out. The cheapest I have found them is at Z1E for $14.50 You can try soaking yours in lemon oil, which you can find in the furniture polish section of the store. That is the only solvent which will not damage the Neoprene in any way and might allow it to go back into shape. When you wipe them be extremely careful so you do not stretch them. You can even BOIL them in the lemon oil. Just be very careful so it dose not catch fire on you while you are doing that. Personally I HATE Keihin carbs and I would not have a set on my bike. If you can, get a set of Mikunis on eBay.
74 Z1-A stock
76 KZ-900 Totaly stock vice MAC pipe
77 KZ-1000A stock
78 Z1-R 100%MINT 500 original Mi.
78 Z1-R Yoshi 1103 kit stage 1 cams Yoshi pipe. Etc
79 KZ-1300 (1400)
80 KZ-1300
81 Scratch built GPz1150R
82 KZ1000
