Just installed a 43mm DR kit on my grande with a polini head. Bike fires up and idles just fine but when I give it throttle it only goes about 15mph. I'm fairly new to mopeds but it sounds like a possible air leak?? I lapped the decomp valve on the new head and am running it without a gasket. Using the base gasket that came with the kit. I also sprayed carb cleaner on the head and base seal and the engine didn't seem to bog down.
Was wondering if anyone knows a good place to start with troubleshooting this issue. (edited)