Cleaning the Stock Exhaust
The service manual tells us to remove the bolt, and clean away. Note: if your tools is not at least 4-1/2" long, it won't reach far enough to do the job.
Others recommend (and I do too), putting the exhaust inside a pile of charcoal briquets (sp?) and then light them up. Wait until the muffler itself is glowing a nice red or red/orange, then take it out. After it has cooled down, then tap the exhaust on all sides, and the carbon can fall out.
What's Inside this Exhaust Anyway?
One Sunday afternoon, being bored, I thought — I'm going to cut apart an exhaust and find out what's inside. The following pictures speak for themselves.
It has been suggested that the muffler's outlet pipe should be made round. The thought is that when made round, it will increase performance. This picture shows that there is an internal pipe, between the two chambers of the muffler, that has a much smaller inside diameter (see the red circle on the right above) when compared to the muffler's outlet pipe (see the red circle on the left above). You can make yours round, but don't expect any performance increases (unless your outlet pipe was crimped almost shut).
Update to this (with thanks to Joe Schuitema) You also cannot just fabricate or swap a later year 80/81/82/83 PA50-II pipe sized larger-header onto a 78/79/80 pa50 - I stock exhaust because the first gen exhausts not only have a much smaller restricted header but that narrowly restricted pipe also extends all the way into both the internal transfers / chambers of the pipe as well making a larger external header pipe useless (unless you replace the interior extension of that header and port additional transfers between chambers and open the exhaust stinger ID all of which is exhausting effort for little to no gain)