Hi,
I use this method to start my 912 uls.
Throttle full off, choke/starting carb activated,engine fires up I disengage choke while advancing throttle to keep rpms at 2100 range.
This process changes little from summer to winter. I do preheat starting at around 50 F or less and the coldest I fly is around the - 5 F (- 15 C) .
The preheat is with a Reiff 150 watt system , and add an insulated cowl cover when the temp lowers .
I am a firm believer of preheating for engine longevity .