Are you running a slide carb or a rotary carb. The novarossi rotary carb is a pain in the butt. The slide carb is just fine. If you are using a slide, there is no reason to switch to an OS. If you run a rotary, the OS is a big help. I know that isn't the nswer to your problem, but I wanted to answer your queston regarding the carbs. I have been using OS carbs on my offroad engines (rotary carbs) for many years now. For onroad, I use slide carbs and the stock nova carbs are just fine.