Agreed, running rich often means the spark plugs will foul with carbon. Then they don't spark.
Dirty air filters can cause this. So, will neglecting the routine 3000 mile tune up these bikes are supposed to have.
Some models have other quirks that may add to "cause". But, you are looking for information without giving any...like what bike you are having issues with.
With all the info you gave us, it could even be a weak, dead battery.
Would it help if we added a round of curses for your bike?