It's a good idea to proportion the amount of choke to the temperature. When it's really cold, so cold you really start to wonder if you want to ride, full choke and switch left on for about 60 seconds to allow the carb heaters to warm up is good. Since cranking speed doesn't generate enough air flow to open the slides, the main jet size won't matter while starting up.
With the Epco pipes, mine will sometimes fire up with a bang, not so much a backfire as just a really hard initial combustion.
