2007-2009 Kawasaki KFX50 service manual, Page 118Get this manual
7CYLINDER HEADVALVES VALVE SPRING INSPECTION Measure the free length of the valve springsService Limit: 34 mm (1.36 in)
Measure compressed force (valve spring) and installed lengthReplace if out of specificationStandard: 19.222 kg at 19.65 mm (0.786 in)