Cold weather starting is nearly always done, & properly so, by using 100% full choke and manipulating the throttle a bit during cranking, as the engine begins to start. Have the clutch lever at the handlebars pulled-in during the cranking to reduce loading of the starter motor by the transmission with its cold thick oil. Helps the battery too.
Many manuals, including the factory Owners Manuals will say to not touch the throttle. In my experience, that is wrong. I have found that most Airheads require some throttle manipulation upon starting in cold weather, and often in mild weather.
As soon as the engine is running, reduce the amount of choke as soon as you can, yet if you need to, and you likely will, keep ‘some’ choke on, until you have smooth running, including when riding. Too quick a reduction may result in the engine dying and needing a restart. Typically the choke lever is returned to ~half-way within half a minute. Even in the coldest weather, the choke lever should be returnable within a few minutes to the half-way position, and not long after to full off …or, nearly so. For very cold weather, try to keep the rpm between 1200-1500 during non-moving time until some decent warmup is had.
Never blip the throttle to high rpm when starting, this is particularly very bad with a cold engine and wear will be high. In some situations you can break rings or collapse an oil filter with a quite cold engine. Generally, you can start an engine & take off modestly, using quite moderate rpm, after 30 seconds to 2 minutes of high idle rpm (1200-1500), if the temperature is down to as low as 40°F or so. I suggest using modest throttle when taking off, and not going over 4500 rpm, preferably not over 4000, until the engine is warmed some, which takes a couple of minutes.