RE: How cold is too cold?
I agree with everything bigedmustafa mentioned.
This would be the only time i would compare a model airplane engine to an automobile engine, if you can get the
darn thing started in that cold weather, once its started it will run fine.
In fact engines will run better in extreme cold than in extreme heat.
If the last time you ran the engine, was in warm weather, it might need a little tuning adjustment.