So i've got a china 80cc 2stroke. When I pull the clutch in and free roll (walking along side the bike at a slow speed) every so often there is a popping or clicking coming from the inside of the engine sprocket casing. The wheel is true, and the chain is tight. I don't seem to notice the sound when the bike is running or when I am coasting with the engine running and the clutch pulled in.. I hear it mainly only when at walking speed with the clutch pulled in... do I have a problem? Is a problem on the rise? thanksss oh and also..., Is it ok to only use the drive chain and eliminate the chain that came with the bike ? It is old and streched and rusted and quite the nuisance while trying pedal to gain speed..