Im looking to pick up a used kit for my friend its a nos brand kit i was wondering if there was anyway to tell if the solenoids are bad can anyone help me out?

 

A quick simple test you can do is to touch the leads from the solenoid to a 12 volt power source. it does not matter which to what they or both black most likley. one to the positive the other to the neg. you should hear it click that is the plunger activating. only do this briefly as the solenoid can over heat and that will burn it up. the solenoid need N2O or fuel flowing through them to cool it.