I have several of these still in original condition other than having been used. I'm wondering if they are simply a muffler or are they 'tuned' any to improve run characteristics? What I'm really wanting to know...is it OK to drill out the tailpipe a tad? I like an exhaust pipe ID to be the same as the net opening on the carb...if not just a little bit bigger on the exhaust pipe. Yes, this does make the engine run a bit louder, but it typically picks up a few hundred RPM, too. Well, what do you think?