So, you put on exhaust and now your bike pops out the exhaust. :(

So you installed an aftermarket exhaust and now you have popping out the exhaust when letting off the throttle. First the Bad News. A small amount of this may be inevitable and its due to that new fancy muffler does not do nearly as good of job as the original did in reducing noise. You see, many bikes pop when chopping the throttle thru the exhaust even with the stock muffler, the fact is you just don't hear it due to the sheer size of the muffler and its sound deadening qualities. Given that, here are three things that can cause or aggravate this problem. 1 - an exhaust leak at the manifold or any joints in the exhaust. 2 - If you're model is equipped with air injection. 3 - Lean carburetor jetting of the low speed circuit.  Fix any leaks first, then plug the air injection if equipped. Lastly try turning out the fuel screw. Good luck!