On Mon, 25 Jan 2016 08:34:06 -0500, "(PeteCresswell)"
wrote:

Per (PeteCresswell):
It's the next day now and it's thoroughly thawed out from sitting in a
heated area all night.

Yup.... Miracle cure. Back to full power and responsive throttle.

But now it is surging most of the time and occasionally backfiring on
full throttle.

This thing must be 10 years old and has never had points or plug
replaced.

Points/plug would be the likely cause, right ?
More likely water in the gas - it'll fart and backfire like crazy
from being too lean. Out some "sea foam" in and open the main jet 1/4
turn. After running the sea-foam through you MAY be able to turn the
jet screw back in again,