Ok, i'll share mine
I'm only 16 so 50cc
First bike was an RS50, fresno system, up jetted to suit, 21mm race carb, k&n filter. Would top at 73mph.
Unfortunately it was the most unreliable thing on earth, never started, if left for anymore than 30 mins it would refuse to start on button and clutch would seize making bumping it an arse. So that went (bought for £550 sold for £800 ..somehow)
But reliability is killed at the cost of speed, and it was ridiculously fast for a 50.
So I then needed something that would work to get me around, found an MBK booster near me, got it off ebay for £210. Parents went and picked it up, when it came back it needed so much more than was described... Was a complete wreck, however mechanically sound.
(the attatched pic is once I had it stripped down so it was easy to work on)
Spent £220 getting it road worthy, resprayed myself, did all the work myself. Took it for an MOT and they fitted a whole new wiring loom (>_>?) that was an extra £90.
But it ended up looking nice, massive tyres make it ride quite nice, was fun adjusting from the rs to it but it's not that bad :] will do a decent 50-55mph. And works always, what else do you need?
(it's the matte black/orange one in final pic :])