I wanted to post this in the tuning section in reply to a question about difficulty in fitting sports cylinder kits but don`t have enough privs yet , short answer : yes you need good knowledge and skill levels to undertake this work , many bike shops get much income correcting bodged attempts to fit these kits and to undertake all the accompanying work that needs to be done such as rollers , belts , final drive kits , carburation , exhausts etc . Despite how these kits are marketed by many sellers basically presenting it as a simple take off bolt on job equalling some staggering power gains this is NOT the case in fact you can end up with less power than you would have had from your stock kit just derestricted , it would take a huge lengthy post to cover this subject properly , but to keep it brief just presuming you do have the skill required you have to think of the cylinder kit as part of a system that all needs to work in harmony to gain the wished for results (I`ve now fitted at least 7/8 so can speak with some experience on this) . So you have decided say to go for a 70 sports kit , right then aluminium or cast iron ? Malossi or Nakaru ? high torque or high revs ? head inc or not ? . Right cast iron vs aluminium , most cheaper kits are iron which is fine but if you can find an aluminium one for around the same money then all the better , it`s lighter and has better heat dissipation properties hence all best kits are this , Malossi vs say Nakaru , there is no doubt Malossii are good , very good , I`ve used them , but , you do pay for the name and can find similar quality and performance for a fair bit less dosh so do some research , read some reviews , then high Torque vs high Revs ? you need to think about how you use your scoot in the main , if t`s short stop start town work then you want good low down grunt and acceleration but if you are blasting up and down nice long A/B roads with not a lot of stop starting then high revs = higher top speeds will be more suited to you , but as said remember that the cylinder/head is just part , the middle part really of a fairly complex system that needs to be working in harmony to achieve desired results, so let`s say you have chosen your kit , now what size carb do they recommend (some say upjetted stock will do , well it will , just don`t expect any where near the proposed power gains) so you find a carb the right size (17.5mm is ample for 90% of sports kits) now you need to find out approx main jet sizes (trial and error for this , start bigger for obvious reasons) this will also be governed by whether or not you are able/want to use original air box or sports filter , big difference to jet size .(you may also want to go for a decent inlet manifold) Right now to other side of the cylinder the exhaust , don`t be cheap there are loads of no name so called power pipes on flebay etc , they are rubbish , depending on the type of cylinder you have gone for you can narrow your pipe search , some are for high end high revving cylinders some for lower revving more torquey kits , so again research and reviews , Pedparts do a very good unbiased guide , unless you have quite an old scoot the stock pipe will have to be replaced due to Catalytic converters and some tricky restriction methods , remember if it`s "e" marked it`s street legal = restricted and will have to be derestricted to work correctly , usually a cone welded into manifold end . So all done ? no not nearly now you need to sort out your roller weights most good pipes come with a set but I would recommend you but a multi weight set and again trial and error will decide , now the drive belt , always worth upgrading to a Kevlar belt if you are upping power, easy , next clutch and torque spring , stock clutches are set up obviously for stock engines so I have always replaced them with a better one with stronger springs to aid acceleration , not very expensive and worth doing , again don`t go mad buying some top end race clutch that will be terrible for road use. Now the Torque spring which governs at what revs/power the final drive is engaged for most sports kits a modest 20% stiffer spring will do , again a cheap item but buy a known reputable brand. Finally (I think) final drive , now this can often be left stock as is manufactured to be able to hurl your scoot along in unrestricted form for world market , but if you have say a Speedfight 100 and are fitting a 120 kit the 100 had same final drive ratios as the 50 and will over rev unless say a pm tuning kit is fitted , bit off topic I know but worth a mention as are performance Torque drivers which can give better power delivery by way of differing the shifting pattern , but that`s getting way out there , so hope this is of some help to anyone tempted by a nice shiny new 50/70 sports kit , it can start with a modest £120 or so and quickly become £500+ believe me I`ve been there. Final thought if looking for a good 70 sports kiit , Airsal 70 sports , all aluminium includes new head and all necessary gaskets etc , cheaper than a cast iron Polini sport and low down grunt and acceleration that will leave revvy high end kits for dead at the lights , great quality and if you shop about around £120 best 70 sports kit I`ve fitted for town use !!
+1 Marky Mark The only problem with that is the cost, as you said. I've lost count of the amount of times I've told the kids that they can't do 'X' unless they do A=B=C first. And when you give them the cost, the face goes blank. The only time I have said that and was stunned, was to the local weed dealer, and he turned round and said "right do it". So I did. On his Runner SP125. Police have never caught him yet.
