The owner´s manual call for B6ES. I got B7ES, which is a little colder. I think B8ES might be too cold for that bike, which means it won´t burn the air/fuel mixture totally and might leave a residue on the plugs. If your bike is an original 82 KZ750 CSR (without rejeting or carb modifications), probably B6 or B7 should be OK. Try reading the plugs to see if the mixture is too lean or too reach, or just perfect. PC