belt

I'm very new to motorized biking, having just finished turning an old 90's mountain bike into a speed demon. (or at least I hope it will be) The kit I got was a pretty standard 49cc 4 stroke from ebay. The biggest problem I've had so far is the chain that connects the belt drive to the sprocket...

i noticed helio has 100t pulley for 4g. if i get it where can i find belts? can i get them from auto parts store?