I have a 2007 Vento Phantom GT5 150CC. I have a little over 700 miles on it and have followed the break in schedule as outlined in the manual. Everything is stock so far, and I am a big guy (210lbs.) So far top sustainable WOT speed it about 47. I have gotten it to 60 downhill with a tailwind, but I thought stock, I should get better speed out of a 150. I run 91 octane fuel, and the only thing I have done is to take out all the restrictive foam blocks out of the air box leaving it with the thin foam "pre" filter and the paper regular filter. Any ideas, or am I expecting to much. I thought these should be doing 50 mph + without to much trouble. Thanks for the input.