I am going out on a limb...but I seem to remember reading some where that this:
"i've also noticed that if i roll on the throttle very quickly that instead of the swift increase of power (like say my girlfriends Scrambler gives) the bike starts to choak, the exhaust pops and then i get a release of power (kind of delayed) - this is usually when it's at neutral."
is a rich condition, too much fuel.....It seems like you have determined by running with the cap off that you are not starving for fuel....
