Mine Did this last year. I tried everything and it didn't get better. I got new rollers, cleaned the carb, new oil, plug, filter. Then I took the top off the carb and found a kink in the spring that wasn't letting the carb open when on the throttle. I would take the top of the carb off and check the spring. Make sure it is not damaged and that it is installed correctly and nothing is binding up with it. I found a new spring that was close enough to make work at a hardware store for 65 cents. It runs like a champ now and cruises at 70-75 gps all day with a top of 85 gps. (I do have larger tires though, so my top speed is a bit higher). its a no cost check and you just need a screwdriver and to open the carb access in the met in box.