Hustlin' Hank wrote:
I need some ideas. It is a Yamaha atv. Battery shows 12.9 volts and
turns the engine over fine, but won't start. When I hook up a battery
charger it starts right up. Battery voltage when running is 14 volts.

Any ideas?

Hank ~~~knows something has to be wrong

Are you doing anything at all differently not related to the battery?
It almost sounds like there is some safety device not allowing the
engine to start. My motorcycle has a couple or so things like that.