Changing jets on a Mikuni carb like the on that that 650 thumper is really easy. Also because the bike has so much open space under the carburetor, you don't even need to remove the carburetor to do it.
Here are two videos I found by googling "savage 650 jet change":
https://www.youtube.com/watch?v=0j-nPtoP2MY and
https://www.youtube.com/watch?v=qpHQk-pA6fI
You may be able to fix it with just jet changes (without adjusting the idle mixture, which involves the use of a drill, something that tends to scare people a bit when working on a carburetor...).