all the big bore kits are made from stock cylinders
when the cylinder is bored the cylinder skirt that fits down into
the case gets real thin and excessive heat can crack them .
a 70cc has a thicker skirt than a 72cc .
for a first time mod a 70cc can be a safer choice, or not depends on how close you
come to getting it fine tuned.
yes a pipe is critical with a cylinder and will help some on a stock cylinder
up jetting is needed with just a pipe and then again bigger with a cylinder.
i'm hesitant with open filters and a first time tuner as you have to always
be adjusting and re adjusting the mix every time the weather changes 12 degrees ,
or it goes from wet to dry, even night to day can mess you up.
heres a link to some TGB mod parts
http://whidbeyislandmoped.com/cart/index.php?main_page=index&cPath=1&zenid=88728db1820ce8b449cb56d695ad5448 oilyhans
i own a scooter shop with rentals ,sales& racing parts.
i also appraise scooters for KBB.
2003 Vino classic stage 0.75
de-reged stock variator w/8g sliding weights.
1.5k rpm springs
42mph
2005 veniceLX ~70cc~upjet~1.5k rpm springs & 7gr sliders
46mph
KeyWest de restricted~8gr slide