Yeah, next time try to remember how tight you tightened it and then stop before it starts spinning the next time. When you are new to working on things it can really save you some time and money to use a torque wrench to reassemble everything. The manual has a torque setting for virtually everything.
How tight did you want it anyway?
The plug misfiring for whatever reason can make an engine backfire as well as the timing mentioned. An eractic kicking motion does it too.