When the 172 is opened, by default, the fuel selector is in the Both Tanks position.  I've primed the engine but that does not work. The Carenado C172 was uninstalled then reinstall to no avail.   If I use Ctrl + E the engine will start.  If I move the fuel selector from the default position to Left or Right tank it will start.  If I move the fuel selector from the default position to left or right tank and back to Both, it will start.  I've also uninstalled and reinstalled the C172 but that too did not work. There are no fuel management add-ons.  I believe this glitch started when I updated from P3D v4.2 to v4.3?  Basically, the engine will not start in the Both Tanks position.  Carenado could not help.

Any suggestions

Thanks, Pat

Lean the mixture and try again.