Hey, if I drilled holes in the baffle of the stock muffler, would that have any affect (worsen) my gas mileage if I didn't re-jet or drop a new carb in, basically if I left everything else stock?

Depends how many and how big holes. If You don't touch the carb, there is not going to be significant difference in the gas milage, but Why make leaner already lean running bike? If You don't have backfiring now, You might get it. If You don't like the stock muffler, buy Yourself some HD exhaust for cheap and install it. If You like it better, sell Your exhaust on eBay and You will make money. If You don't like it- You can always go back. Once You drill holes, You get something,that You can not even sell. How do You know how many and what size holes to drill?

shawn_b wrote on 12/31/69 at 16:00:01:

Lean and rich both refer to the fuel/air mixture.  Lean is too much air (or too little fuel) while rich is too much fuel (or too little air).

He's saying that drilling holes is likely to increase airflow, making the mixture leaner... and the bike is already quite lean when stock.