Yes the governor probably isn't functioning correctly or is removed because I did some math and in theory, with a top rpm of 3600 and 6:1 gear ratio, 15" tires, top speed should be 27 mph. 5000 rpm would be 37 mph.
 Post added at 09:14 PM  Previous post was at 09:10 PM 
Wait I just looked at your tires and they are 14" so my math is a little off but still pretty close.
25 mph at 3600 rpm and 35 mph at 5k rpm
