Check for stiff links.
This is even more likely if you joined the ends using a chain tool rather than a special link. To rectify it, hopefully your chain tool has two pairs of 'teeth'
One pair is for joining the chain. This will have a plate that stops the chain flexing as you push the pin in. The other pair won't have this support. They are used for loosening a tight link. Just tweak it from the opposite side that you joined it from.
Sorry if that reads as jibberish or if you knew it all before hand!
Edit! You're sorted then! I didn't see the second page. Looks a cracking bike judging by the rear mech and wheel!
I did skimp on the chain - was in the sales at less than £10 - it's KMC but it's not what I should of bought - no special link! chain tool was properly cheap and that's headed for the bin - it's for track chains so doesn't hold a multi-speed chain properly so had to employ tensioning plyers to hold the chain in place whilst I lined up the grommit to the hole! what a faff. If you know of a decent chain tool let me know as I really should invest in one.
bike has gone over budget thanks to the wheels but i'm pretty happy with it so far - no good for windy days though!
thread is here if you fancy a look - http://www.retrobike.co.uk/forum/viewtopic.php?t=234479