400ex wont start - need help

[tmtracing]

i traded for this quad a few weeks ago. ran great, then started knocking pretty good the other day. stopped riding as soon as i noticed it.
tried to start it today and it wont start. i am not new to quads but not an expert.

need help. any help would be greatly appreciated.

thanks in advance.

[mark_6516]

could be a lot of differnt things check to see if you got fire if not it my of jumped time and bent a valve. will it turn over ? really need more info