After finally getting my bike running and taking a small ride maybe 5 miles or so the chain decides to fall off the sprocket. I notice in my haste to ride my bike I failed to check the great stock tensioner. Anyway I get it home and was able to put chain back on, tighten tensioner and now it won't stay on. Ive searched for info and cannot find any. I know I'm a "newbie" and am probably doing something stupid. Please someone, anyone help.