troubleshoot

Had this bike built by a guy a fair while away from me, and less than two weeks later it's just stopped working. Managed to run half a tank of petrol, refilled and now the motor won't kick back in at all. The guy refuses to help me or take responsibility. I'm not great at things mechanically...

This all started back when i was reading this: http://motorbicycling.com/showthread.php?t=36334 So after reading up on that forum, i decided to change out my piston pin bearing (by this time, my bike had a little more than 500 miles). So i bought this...

I have a 66cc that's been running great for 2 months. Out of nowhere today it just started losing power when climbing hills or running hard. Starts up fine and runs well when idling or putting around. But as soon as you start to climb it goes, then sputters, goes, sputters, etc. I am certainly...