Sounds to me like just a small adjustment is needed.

A "tweak" of the mixture screws should help for those with stock exhaust. For those with modified exhaust the jet & shim thing along with K&N filter.

But whenever you change things, you will need to "tweak" again. Fastfred, once you changed your pipes/mufflers then a little adjustment should do the trick. Besides your mixture, make sure the RPM's are high enough at idle too.

Check your plugs. Have seen them foul up quick, from folks using the "choke" too long after starting. Close that thing as soon as the bike will let you.