I drilled some extra holes in the end cap, because I'm a little suspect of a pipe coming out the back that is smaller than the opening at the motor- it seems really tempting back pressure poor performance to me. It did make things louder, which is unfortunate.
Then the friggin end cap fell off on it's own riding, I couldn't find it, and it seemed really too loud then. So my solution, posted this summer was to extend the muffler with an aluminum can (I use long 16 oz beer cans) and I drill holes in the end, which replaces the end cap, and makes the whole thing really even more quiet than stock. The can is held on by a radiator hose worm clamp.
Just how much difference it makes was evident one day when it came off. It was VERY much louder when it did. It is best to cut some seams lengthwise wher the can goes over the muffler so it overlaps itself a little and does not crimp. At first I used TWO cans and re-covered the whole muffler, but that kept a lot of heat on the muffler, so now I just use one, overlapped on the muffler end an inch or so.
I bought a chrome extended muffler and pipe from boygofast on ebay, but it won't fit my cruiser with oversized down tubing. Now it looks as if that WILL fit on a Scwhinn Wordl traveller I'm building, with normal size tubing, so I'm real happy about that, because both the pipe and muffler are considerably longer, and I know it will be quiet now, especially on a smaller 50 motor. And I can use the chrome muffler in the kit now on the cruiser- I'll probably still stay with the beer can extender, because it's quieter.
happy motoring