I have done some mods to the stock exhaust.
I started with what I believe is called the stage 1 mod. I grabbed a 3/8 piece of bar steel, and basically sharpened the end. Then I made myself a jig that would hold the bar directly in th centre of the upper exhaust exit. Gave it a couple good swift wacks with a mini sledge. Then did the same for the bottom. This was to create a pilot hole for the larger bar. I grabbed some 5/8 bar steel and sharpened it the same way. Then I grabbed a larger hammer. and proceeded to wack the shit out of the baffle. did the same for the bottom. Then in order to gain a little more rumble on the idle side of the throttle. I drilled two holes at 3 and 9 o'clock in the rear baffle. I started with 3/8 then moved up to 1/2 I may bump it up to 9/16 next.
No carb adj. is necessary. and it REALLY makes a difference.
Next I may go a little deeper (to the next baffle) the first dtage is about 19" and 9" inches in from the tip.