150cc GY6 speed issues?

So my scooter maxes out at something around 30mph.. it use to get up to 45-50mph. i was having issues with the carb and i thought i solved it but now im having problems again. it wont even get past 30mph and it starts bucking, bogging, what have you. its not a violent jerk like it was the first time i had a problem.. it feels more like theres a limit on the speed now. Should i take the carb off again? I should also mention im having issues with the odometer/speedometer no displaying the speed.