Had a lot of bikes. All fuel injected. 1 carbed but didn't keep it long enough and didn't experiment with it. I have run all my bikes with the muffler off to see what it sounds like. Some sound great, some not so great but all sound much louder.

Here's my question, thinking about getting a 08 ninja 250 for ****s and giggles. Definitely putting on a slip on, just a slip no full exhaust. Dealer says I need to rejet and blah blah blah. WHY? I am just taking off the muffler no air intake mods, just want to cut the muffler off 1) too quiet and must make more noise so others know that there is a bike around 2) Cutting it right off to look a little more like a gp style exhaust. If you look at the exhaust on the new 250 it would cut off just perfect.

Why would I need to rejet. When the air in will be the same. Does it need more back pressure in carb applications? I thought that was more important on 2 stroke motors and not 4 stroke.
Any thoughts.

 

you are improving air flow. more out changes whats staying in the cyls. you can usually get away without jetting for slip-ons but more than that you will need/want them to keep your bike happy and living long. add a K&N or other fancy air filter and you changed the air flow again. every little flow change like that can affect how these high performance engines operate. lean means heat and rich means carbon/gunk buildup. too much of either and you have an unhappy engine. heat has the piston melting habbit and the carbon has the sandblasting/wear factor.