2007 yamaha 650 v Star.I am thinking of putting on a set of Vance and Hines short shot.Do I have to rejet?

With long baffles probably not.Without baffles probably.Straight pipes without baffles are the worst possible choice for a street bike though.Engines need back pressure to run properly otherwise they scavenge fuel mixture out of your cylinders making your bike run like crap.|||I'm not positive about this but I don't think you have to. If you change the air filter to a higher flowing one like the K%26amp;N then you would need to re-jet.