Yer buddy sounds like he didn't het it right. I can kit my bike and have a huge exhaust with a stock carb. First off, find out if you have the 2 pipes in your baffle. All it takes is a minute.
Yes, have jets handy if you do anything to the pipe/airfilter. I drilled the noise/flow baffle that looks like 3 tennis balls at the end of mine and it got lourder and faster but 4 strokes now. Meh.