I had a ‘98 ZX-9R with those horrible Tokico 6-piston calipers and they were terrible for binding. Ultimately the only cure was to strip the calipers and remove the pistons individually to clean them. The previous owner claimed to have only ridden it once in winter, but upon closer inspection that single ride must have been across the entire width of Siberia. Under the fairing it was truly gopping, and the brake calipers had suffered from road salt attack. The piston seals had to be removed (do it carefully and they can be used again). Salt corrosion in the seal pockets was forcing the seals hard against the pistons, stopping them from retracting when the brake lever was released, this causing the binding. I made a special tool to clean the salt crap out of the seal pockets and used special brake caliper grease on reassembly (it’s the colour of cherryade, normal grease could cause the seals to swell, leaving you back at square one). The pistons showed little salt damage, and there was no further binding.
They aren’t great brakes at the best of times, if you don’t fancy the faff of a stripdown it might be easier to see if the 4-piston calipers from the later E-model would fit.
