I just got my bike from Spooky Tooth. It's the new Desert Rat with a 4 stroke 50cc. I filled the gear box with 90wt gear oil per the recommendations and I'm finding it really jerks hard when I'm coming off the throttle. It sounds like the gearbox is binding up inside. So far I just been getting her broke in, but the fastest she'll do is 18 mph. I am 6'1" and weigh 190lbs. I was hoping for more around the 30mph range. Does anyone have any helpful tips on why my gearbox may be binding and how to milk a little more speed out of my motor?