It sounds like the carburetor problems. Check and see if there is any air getting in around the carbuetor intake side. While the bike is running spray starter fluid around the carb intakes. If the rpms go up, then there is an air leak.
Otherwise, your carbs may be out of sync. You make a simple carb sync tool by following the directions here:
$1.55 Carb Sync Tool by Marty Ignazito