if all youre getting is 85km/h then you need to sort out your current setup before looking at performance parts, you should be able to clear 100km/h quite easily. check the points (and point gap), timing, spark plugs (and gap), and fuel mixture. you could also make sure the fuel pump is working properly.
it might be worth doing a compression test if none of that helps.. you could also check the coil, do you have an original duel coil setup?
hopefully just adjusting things up will fix it for you.
my friend and i drove a niki from adelaide to surfers paradise, we did between 90 and 120km/h most of the way.
something else that improves top speed but will lower acceleration, is oversize tires.. the niki we drove had them on it, mine doesnt, mine does about 110 before it starts to rev a bit high for comfort, his does about 120+
it depends what youre after. i prefer low speed agility.
