It spits and sputters at the low end and takes forever to reach wide open throttle but once it does it cruises at 35mph without issue. I don't stay there because my engine is still new. It's a stock 66CC motorized bicycle with stock settings. It wasn't doing this initially but now that I've traveled maybe 50 miles with the same gas it's starting to bog down for some reason. I haven't changed the ratio from 16:1 either. My spark plug is not dirty at all. It isn't dirty white, happy brown or sad black.