I doubt that posting this, that the bottom of this problem will be solved. As a bicycle store owner for over 12 years and a mechanic for many more, I believe that if you are not able to figure out why the chain is jamming I can not imagine how someone on this forum will know (especially without even seeing it). I would though, recommend that you take it to your LBS and give them some hands on with the bike. (something that will never happen on this forum). hope you figure it out. Good Luck.