i had an electric carb heat on my jab powered xair. i doubt if it would have helped start the motor, they don't heat up that much ,also i would not want to draw extra current before start up. My battery was marginal because of the long battery cable run. started on frosty mornings no problem at all. as others have said, you must be at idle position to enrich the fuel mix.
even cracking the throttle a little bit will prevent starting.