Hi guys, I recently purchased a 79 cx500. I've taken it out on the freeway recently and at about 6-7k rev's I'm only sitting on about 50mph. It has a custom exhaust with a muffler with the baffle removed. I was guessing the lack of back pressure could be the reason for the lack of power? Other than that I think the carbys need a rebuild as there is a slight leak.. Any advice or help would be much appreciated, as this is my first bike and my knowledge is quite minimal..