Okay I recently bought a "80cc" motor for my huffy beach cruiser. It was an engine from eBay from China or something. I spent 4 hours putting every single piece on. When I rode it the chain would get very hard to move then make a snapping sound but nothing would snap. Just the chain would pop off. (The clutch works fine) when you roll the bike and the chain moves you can feel in the little gearbox that holds the sprocket start to tense up then finally make the snapping noise. Any ideas what's wrong?? My chain is very tight on it and it rolls fine up until one section of the chain. Please help!