Cateye top speed?

I recently traded my electric pocket bike for a cateye that needed some work. It was in really bad shape (wouldn't even start), and now it starts and runs, but not perfectly...it goes about 13-15 mph. About how fast should it be able to go with stock parts? Rider weighs about 125 lbs.

My X2 which is similar to the Cat-Eye tops at 30 mph down hill with the wind pushing., I am about 145 pounds

ok thanks the day after i wrote that post i messed with the carburator and now its going at about 25. (flat ground, no wind