I got a question here that my friends and I have been arguing about. When changing exhausts, is it necessary to re-jet to compensate for the change in backpressure? Any helps thanks

Rejet? I dont know about that, maybe to gain more power but with a couple fuel adjustments on the carb and you should be good to go. fuel injection is a little different, there is a wiring mod or you can buy a power commander...but definatly only need to adjust the carb right to make it run perfect, rejetting would be a performance increase

Depends on the exhaust work.

A slip-on and you could probably stick with stock fueling.

A full system and a jet kit is a must.

Aftermarket exhausts give you increased exhausting ability which in turn makes the motor lean out. Problem is bikes are lean to start with to keep them EPA friendly. Even with a stock can you can get improvements from more fuel.
The upside to going with a jet kit is somebody else does your homework. You don't have to sit at a shop with a gas analyzer trying to measure exhaust O2 and CO levels to figure out if your improving. Or take a hundred plug readings after you change your air/fuel and richen screws a quarter turn. No, you open the box, look at the chart that has temperature and altitude settings and then change the main and pilot jets. And reset the fuel screw to whatever the instructions say. Button it up and you done. No probs.

yeah i put a micron highmount slip on my 99 r6 and i havent had any problems. anything else like a k+n or full systems yeah you will need to have it re-jetted....