That's how mine starts every cool morning. It fires up, then idles a little slow then revs up to a fast idle for a moment. If you are referring to it CRANKING slow that's a different issue. But if it still cranks fast; well then that sounds like how it's supposed to work!
Some people don't like it but I do. Namely because my wifes bike is also fuel injected but does NOT have a fast idle. While it's better than a carb, it's rough when cold. Rough to start, idles a little rough, and is easy to kill until it's been running for a minute or two. A 'side affect' of the fast idle is that it's running a bit higher RPM so it runs smoother and goes easier when cold!