Pipe is on fire, please help!

[Stock 400 rider]

Hi, I need to sell my quad today and I`m not sure if I sell it with or without the pipe.
On the last ride I was heading to the woods when I saw the inside part of the pipe on fire. I turned the motor off to let it cool but when I started again it was hot and red and hell.

Any ideas of what could it be?

Should I sell it like that or put the stock back? I don`t think he will like it stock.

I need to fix this pipe.

Thanks.

[krt400ex]

ummm, well did u jet the bike when u put the pipe on? and did the bike ever run this hot before?? or is it just been the past few rides?

[mattonln]

sounds like your packing is coming apart and catching on fire before it blows out. just repack the silencer

[brazilian rider]

Yeah I think I need to repack
Thanks a lot