chain jumping when in gear...

[Dead Eye]

I've noticed that when the bike is cold the revs aren't perfectly stable until it warms up a fair bit. Even then it flickers about a little which is more than likely a sign of needing the cards balanced. This up and down in the revs will causes excess pull on the chain and cause it to jump then not because the tension has dropped - I can't see it being a problem. As someone mentioned before, when the bike is on the ground and loaded it up, there is a significant amount of force on the wheel which mostly prevents it.