Cut the exhaust up 2.7mm, widen it to 24mm and in an oval shape. Cut the intake down 3.7mm and widen to 26.4mm and you can do it in more of a square shape. Leave the opening round for the intake though, and make it smooth from the opening to the square part on the piston side. Cut the top of the piston dome down 1.8mm on each side, this opens the transfers up earlier. Buy a 50cc hi hi comp Puch head and bolt it on. This sets your timings up to around 155 exhaust, 140 intake, 115 transfers. Run the stock carb with a UNI pod filter, 72-76 main, 35 idle, 210 diffuser and set the needle second from top. You'll be good then.