1987 TRX 125 starting problem

Well gentlemen…. this thing is going to be the death of me…. Carb rebuilt, neutral safety switch by passed,CDI box is good. All grounds are good.On a good day it will fire right up and run all day. But somedays it will fire and after I go to try and crank it over again no spark. If anyone has identified the fix to this chronic issue please let me know.