I am buying my friends 08 honda 400ex and he has a slip on pipe. do you have to re jet the carb for a slip on?

 

I' sorry it's an 07 400ex and its a Carbon Fiber HMF Bill Ballance Slip on. So would i need to rejet?

 

If you only do the slip on and not an air filter as well, you will probably not need the rejet (but why waste time putting on a slip-on without improving the intake?)

 

Is there any particular way to tell if you need to rejet?

 

You should check your spark plug for the color. White deposites = Too lean. Black = too rich. you want a nice golden brown color you should be able to find pictures on the internet of good and bad plugs and compair your to that.