I have a 1993 Tomos Sprint. I recently changed the cylinder from an a3 cylinder to an a5 cylinder. I noticed it wasn't starting or accellerating right. When you pull the throttle back, sometimes it wont go, or sometimes it will die out immediately. I thought that it might be something wrong with the carb, so I changed it, but it is still doing the same thing. I think it is that petcock, but I am not sure. Anybody want to help please do.