do u put the choke back in before u start riding?
i have been told not to apply throttle when the choke is open.
5 mins sound too long to me, i only open the choke only when it is really cold,
start it up with choke and leave it for about a min, push the choke back in and apply a bit of throttle, rev to around 3000rpm and let it idle for another min and it's ready to go.