You need 10 posts before you can post pics or links.

As far as the muffler, and set up, yeah look at the links felker posted. The YS engines are a bit different, and are very much powerhouse engines. Once you get the plumbing and starting procedure learned, the best tool you can have for 4-stroke engines is a tachometer. Search and study how to best tune them... and they will run very well.

I won't go into any detail here, mostly because alot of it is explained in those links provided Mr. felker. Study those and then come back if you have questions. Post up some more to get your 10 posts, and then you can post pics of what you have.

The YS mufflers aren't huge by any stretch. You can't compare them to a standard 2-stoke muffler.. they're half the size or less then that. Some die hards actually just run a straight pipe and no muffler, and they actually aren't much louder(the muffling with stock YS is minimal), and generally 4-strokes aren't nearly as loud as a comparable 2-stroke. That's one of the appealing things about all 4 strokes.

It does sound like you have a decent engine there though, just be careful with it... and study... and if you can find someone near you with first hand experience that's your best bet.