Warning long boring post that may help save time and money ! Over the years I have been a member of several scooter based forums and learned a lot along with the fact that I have owned a dozen scoots , all 2 stroke. All modded with 70 kits(except Italjet 125 twin , a mental ride). My favourite every day ride kits being the Polini and Airsal 70 Sport kits (do 90% of my riding in town/suburbs ) Favourite balls out performance kit being the Malossi MHR Replica. The first kit i bought was an early version of the Polini Evo , also my first mistake(scooter tuning ) It eat my crank shaft within 6 weeks , would have been quicker if not for running in ! Only after this and the fact that i never got it running right (only good WOT) got me actually researching what i was throwing my hard earned money at . What i discovered was that despite being what would seem a relatively simple design it is in fact a clever balancing act that is very easy to upset and that there are no just bolt on and go power upgrade parts that do not require other parts to be upgraded or changed to keep it in balance. I wish that i`d known this when i had bought that Evo kit . The stock Minarelli crank is a very good bit of kit and fine for 70/50 Sport kits but won`t last long if you are regularly going to hit 9500+ rpm and is really best for around 8500rpm so a kit like the Evo that will hit around 13000rpm requires a crank shaft that can handle the revs and the power which can be up to 4 times stock and more. I rebuilt the engine and despite it being a costly time consuming job i learnt a lot early in my time as a scooter owner , still learning , never stops ! So really what the message is that take some time to think about how and where you ride , WOT on a restricted scoot won`t equal WOT on a 60+ mph scoot , most owners are using their scoots in or around town so 55mph top end is fine , what is much more important is acceleration and low down torque (good brakes too). So Sport to mid range kits are best, Sport IMHO being tops for town. The top end racing kits are astounding 20+ BHP when right set up is used and speeds of 65+mph but at huge revs and not happy stop starting in town(hence racing in title or description) What many do not tell the buyer is that a total rebuild of engine , transmission etc is required and deep pockets too. Bolting on a 70 kit is child`s play , replacing a crank is NOT. Carbs are also misunderstood , you do not have to buy huge 21/23mm carbs for most kits , in fact many are happy with a 17.5 maybe a 19mm , lower end kits are fine with up-jetted stock 12mm carbs. Pipes too are fussy about what rev range you are going to use them at , some only coming into their own over 11000 rpm so useless on a Sport kit , others make all their power at say 7500 rpm so just the job for a Sport kit. Rollers/variators , torque springs and clutch springs are a real dark art to master with rarely a few people having same optimal set up , just your weight playing a factor. Buying a multi weight set of rollers , clutch springs and torque springs does not cost the earth and allows you to fine tune , mixing and matching as you go .Clutches too are important , boring but need to be got right , often the stock clutch with stronger springs will be great , Jasil do a good set of clutch springs which are rated +15% +30% and +50% so their strongest same as many other brands weakest, great if you don`t want to be having to 5000+rpm to pull away and having the gearing shift to high when you want low. Final drive gearing is often fine stock as most designed for unrestricted 45+ mph scoots (minarelli anyhow) I have only changed final drive gearing twice , worked good on one scoot but was too high except when WOT on main roads on other and both sacrificed some low end grunt for top end gain , so again where are you using the scoot most ? Sleepy now ? Good but food for thought , just remember it`s a finely balanced system , so when thinking of making a change to it look at what that will effect and research what`s needed, PedParts have some great blogs on tuning , well worth checking out. Good luck.