Wont be the CDI. Give it more fuel down low. Turn the low speed mixture screw out a turn. Also, check the plugs are the correct ones. If they are too hot it will run lean. I think they run BR7HS's but you should try some BR8HS's to cool it down. If you have the same problem again, put a bigger low jet in and try again. If it keeps doing it, the timing may be slightly advanced. You can rotate the stator back a couple of millimeters.