Ive had My 1980 express for 14 years and the motor was pretty beat never got to ride it untill I found a 77 motor on ebay for not too much money a couple weeks ago. found the stock pipe sucked arse, I had a spare pipe so I decided to try a pocket bike chamber on the header. I had the pocket bike running with the pipe and it never sounded right so made sure to check if the header pipe on the PB chamber was extended in to the cone. It was by 2". I cut the pipe out took the 2" off rewelded and the PB header pipe fits over Express header pipe perfectly!!!. Pocket bike chambers are easy and cheap to get but you may have to remedy what I had to in order for it to be effective.
My welder is really starting to pay off now :-)