I've had a stock black and stock chrome pipes. The chrome one I gutted and it ran pretty good. I put the chamber on because it looks mean. It seems to have a little more torque.
I also got some port work done and I re-work the stock carbs. I take a bit and make the rear bigger and add a taper to the rear of the slide, then I put on a cartridge roll and clean up the whole bore. Makes the cheap carb flow a lot better. I got some pics of the stock and a re-worked carb side by side.
Here's a tip when putting a slant head on a 80(66)cc engine with the 6mm studs. The slant head has holes for the 8mm studs so it will be a sloppy fit on the 6mm studs. I got 4 dowel pins off of a CB750 clutch cover and put them in the head holes for a nice fit. Any dowel pins that are used for 6mm bolts on about all jap motorcycle engines will do the job.