My son was riding his 2006 ktm sx 50 senior today and it was fine.He rode it for about 30 minutes and shut it down for about 2 hours.He wanted me to fire it back up for him to ride some more and I couldn´t get it to start.I change the spark plug thinking that would do the trick but it still won´t start.We have only had this thing for about a month so are new to these things.Please help!