Cindy, first remind us all of what intake/carb you are using.

Are you taking these temps while idling? If so, try checking the temps at 2000rpm as well, and see how they compare side/side. You might be surprised.  Depending on the intake/carb set-up, a lean idle mixture to one side could explain the temp differences. An intake manifold gasket leak would do the same. Post the numbers for each header tube for us, so we can see the difference. If the engine is idling, and running fine, you may be chasing a ghost here.

One thing I could think of but cannot think of a reason why it would happen would be that that side is running leaner then the other.