So here’s the story… I bought a gy 125 a couple of years ago off a friend’s son. It was only 3 years old but he had trashed it so I got it for only £100. I sorted it out and put it back on the road to use for a bit of green laning. I fitted the gy 125 (OHC) with a foam performance air filter and noisy pit bike muffler. It ran well when I sorted the jetting but I wanted more power so I fitted a 144cc barrel of a Honda cb150. The Honda engine has the cam chain tensioner at the bottom end so I had to make my own and fit it to the side of the barrel. Once I got this engine sorted it ran very well, it would stand-up wheelie in 1st gear and top out at 70 mph. (I have kept this engine!) I then came across a good value new gy 200 OHV engine off a reputable dealer. I fitted this engine hoping it would give a bit more torque for off road riding but still give a 70 mph top end. I originally ran it off the pz26 carb which I ran the gy 125 / 144 from. I had to lean it right down to get it to run right due to the increased vacuum. It pulled like a train in the mid-range but would not pull at all at the top end. I decided to fit a bigger carb, the pz30, and here’s where my problems started!! I cannot get it to pull from ¾ throttle. At 3/4+ throttle In low gear it miss fires and is generally rough. In high gear it’s lifeless. The pz30 carb came with a #104 main jet and I’ve tried a #105, #115, and #95. Nothing seems to improve the top end. It’s totally lifeless with the #95 and miss fires even more on the #115. There was no improvement on top end going up or down. Still lucky to get 50mph. For information… The bike idles beautifully. The plug is light tan. I changed the oil at 150 miles and it was clean. I re-set the valves at 150 miles, they were tight. This had no effect on performance. The compression test gives 140 psi. The spark is a weak blue when I crank it over and I’m going to fit an iridium plug when it arrives. I have discounted this as a problem as it idles so well and run well at mid-range. Does anyone know then standard card size for a GY200? The standard jetting for the GY200? Any other ideas…..????? I know I could refit the old engine but I really want to get this one sorted!!