2009 KLX250S with Bill Blue 351 kit, pumper carb. I am trying to remove the muffler cap. I got the set bolt on the bottom out but the cap not budge. I have a different, larger diameter opening cap, (pictured), to install after I modify the OEM muffler cap, the new one will bolt over it. I am also trying to decide how much of the guts should be removed from inside the can.

Thanks Mick

 

On a stock muffler?
I believe the bottom bolt is a plug for flushing out carbon.
The cap is not made to come off.
If you do this, you'll most likely destroy the spark arrestor function, which renders it illegal (and unsafe) for lots of off road riding. And unless you remove lots of guts, your efforts will do little to improve performance.
Those that did what you're trying often took a hole saw to the cap. Still, little to any performance gains.