Exhaust extended

It won't hinder performance at all. If anything, it'll improve performance, especially if it's a 2 stroke. See, 2 stroke engines need a lot more back pressure from the exhaust than 4 stroke engines, and you can tune how much exhaust back pressure there is in a certain RPM range of the engine by lengthening or shortening the pipe from the engine to the back pressure source, in this case the stock muffler, and this changes the engine's powerband. If you lengthen the pipe, it'll make the back pressure happen later, which will make the powerband peak at less of an RPM. Here's a gif on how this works in a 2 stroke engine: http://i54.tinypic.com/2cqkz8h.gif The blue is air, the green is air and fuel mixed together, and the gray is exhaust. As you can see, some air and fuel escapes into the exhaust system, and the back pressure provided by either a muffler, or in the case of that gif, an expansion chamber, pushes that air and fuel back into the engine to be burnt.

Sometimes it will restrict the power, sometimes the power will increase. I built my own exhaust from 1/2" conduit. I ran open pipe at first, noticed a drastic drop in top speed and an obnoxious exhaust note. I then welded on a 3/8" washer to the end of the pipe to bring back some backpressure and the top speed increased by a lot! I welded on the stock muffler to the end (left the washer on) and only lost about 1 or 2 mph. It dropped top speed down to 43 mph on a mostly stock 48cc, so I cant complain. I guess you'll just have to see what it does.