2001 mercury 250 pro xb. Running rich. Bad hole shot now. Throttle response not what it used to be. Reduced too end rpms. Have checked the basics such as compression, spark. Just had injectors cleaned and flowed. Vst cleaned. Regulator screen checked and cleaned. Thermostats changed. Checked tuner for cracks. Sensors checkd. New Water separator fikter. Rebuilt low pressure fuel pump. Supposedly reeds were checked and looked ok when they cleaned injectors. Might have to look at them myself. Im down to checking bleed line check valves next. First question, can bleed line check valves cause all those issues? Any other things to check ?