What sort of mods do you have now? 5's could be to light of a roller... IF you went from the oem 8.5 down to the 5's then yeah, to light.. If the scoot is basically stock, try some 7's, 7.5's... Stock, those helped me. of course i have ported things, jetted several times and i was running 5.1 malossi rollers before i tore her down for this build.
May need to check the main spring also? a malossi 1000 white spring is good for a stock zx also(still have 1 in mine). Hope this helps...
p.s, get a roller tuning kit, then you wont have to buy all the rollers, tune in and get the size that is best..