we have a solo-hirer of our PA28 who complained of rough running when doing the power checks and called it a day saying the mags were playing up. when i went out and had a quick look at it, i noticed that the primer was unlocked. i started it and had no problems once the primer was locked.
with same hirer on a different day, we had to go out to the apron and explain why it sounded so bad when he was taxiing. some people just like learning the hard way....he just didn't listen the first time.
don't want to think what would of happened on take-off to him if he had not done proper power checks....we are reviewing his situation as i write this