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How to make my rs125 faster

Discussion in 'Modifications and Projects' started by syd rs125, Dec 28, 2007.

  1. I know alot of people are gonna say just upgrade but i love the rs125 and i would like to get about 10 more bhp out of her i have read alot of UK forums and all i can find in common upgrades are 34mm carbs and new expansion chamber how much would this increas the power and what else could be done for a significant power gain??

  2. Want it faster or just more power?

    Full and lightweight exhaust
    Strip any unnecessary weight
    Upgrade suspension front and back and get it adjusted to your height, weight and riding style
    Upgrade air intake, more free flowing exhaust
    Dynotune & rejet to get advantages from above stuff
    Learning/Track days to get more skill and confidence to go faster

    Anything further than that (ie engine mods) will turn it into something very unreliable imo and will need far more regular rebuilds. If its just a fun short weekend ride/track bike go for it, but if you need it for transportation at all don't bother, seriously. As for what you'd do if you don't care about costs or reliability-bigger carbs is a start, and the other general engine mods but I won't try to go into them as I don't have a firm understanding of that.
  3. Mate, it only generates 33hp

    What you have read is about the UK power limitation laws which limits young riders. RS125 is the learner legal (in 14.6 bhp form) which is restricted by design.

    The extra power is seemingly gained by the de-restriction process.
  4. Should be noted as well, that 10hp from a what, 35hp bike is an ENORMOUS jump. Just wanted to stress that so you get an idea of how little gain in power you will get for the reduction in reliability. For that reason if I had your bike and didn't want to upgrade I'd just get a new filter and full exhaust, then rejet. I'd then improve suspension, get braided brake lines and better brake pads and do some track days. These mods all up could cost you as little as 1600ish if you got everything at reasonable prices. But getting extra engine mods, you could add 1000-1500ish pretty easily.
  5. Lots of things.
    expansion chamber + end can will make a fair bit more with a rejet.
    High compression heads
    Extreme porting (rs125 have fairly agressive porting stock)
    Big bore kit

    All cost money, and some knowledge.
  6. shove a CR500 engine in it....or a CR250 engine as CR500 engines are a bit scarce
  7. Something like this:
    Might come close to giving an extra 10hp.
  8. WOW quick replies thanks guys lots of good info there.
    The handling of the bike is already damn good the forks have heavier oil i could probably have the rear fettled with a bit the brakes are fine as standard. I have read on the aprilia forums that changing air filters or using cone filters only changes induction noise and does nothing for power.
    Track days are already on the agenda. I woud like some good performance mods without affecting the reliability too much but i don't mind spending up to 2000 on the engine and later on when i want to upgrade i can turn this bike into a track bike.
    So for $2000 what would u buy to get the most out of the engine??
  9. Then forget the engine mods. SERIOUSLY.

    When its strictly a trackbike, or a <5000kms a year bike, then you might like to do the engine mods.

    + doing engine mods generally reduces resale as people know you've thrashed the crap out of it and that its more expensive to run and maintain. I'm assuming you dont have fulls and thus can't get a bigger bike yet? The few thousand you'd spend on giving your bike a FEW more hp will buy you half of your next bike.

    Why the need for more power? You can just substitute power with skill - look at the motogp different categories, the 250cc bikes are only a few seconds behind the big bikes, and the 125cc bikes aren't that much behind the 250s.

    Being such a light and agile bike you only need to get up to a decent speed ONCE, and then just maintain fast corner speed.

    If you need to accelerate hard from a stop alot (ie green light warrior) then you've just got the wrong bike. Maybe play with the gearing if thats the case, and wait until you get a bigger bike..
  10. no acceleration is fine but when powering out of corners the bike feels annemic "think i spelt that right" i know the bike is not designed to pull hard out of corners but rather to have a higher entry speed but on the road that can be a bit suicidal.
    just feel like i need that little extra poke.
  11. So make sure you come out of the corner near powerband? Even on my 250, if you kept it near the funzone you could accelerate nicely out. I suppose you do lack alot of torque though.

    If you want the engine mods thats cool and fine of course, just trying to make you aware that there will be considerable cost, extra problems, more expensive to maintain, not as reliable, worse resale - all for a liiiitle bit more power. To help make the decision go ride a 600cc bike :) You'll realise even 10hp more is sfa in comparison to what lies ahead..

    Do the cheap power mods such as exhaust (and maybe bigger expansion chamber), air filter then rejet. Will give you a few more hp after its tuned.
  12. get the revs up higher, and maintain them through the corner.
  13. You have a good point Phizog playing with the engine only after it has strictly become a track bike would probably save me money in the long run.
    i should probably get the suspension set up properly who in sydney is the best at sorting suspension??
  14. Anywhere that advertises a specialty in race set up will be able to sort you out, whereabouts are you in sydney? Luckily for me, my local mech does race prep :)
  15. I'm in the city but don't mind travelling. anywhere in syd will do as long as they are known to be good! How much roughly am i looking at to get the standard suspension set up for me??
    Hmm i should probably change the subject name
  16. Depends what you're looking at getting done. I don't know in which ways the rs125 is adjustable? Even if it was fully adjustable, if you were just getting it set up for you.. I'd say half an hour labour -ish. Probably 50-70ish.

    But if you are going to get some work on the front, like changing springs, emulators, etc. anywhere from 150-700 depending on how much you get done. For the rear, anywhere from 100-1200 (ie anywhere from substituting a better shock to getting a brand new after market ohlins shock).

    I'd go to a handful of shops that do the work and talk to them about what your options are.
  17. suspension setup seems like a bit of a black art to me i will have to find some guru swamby f#@k master to explain it all.
    the forks arent adjustable as far as i know but they have had heavier fork oil put in but when i asked the mechanic who was the owner of this bike before me if i should go for some stiffer springs because of our weight difference he was about 70kg and i'm 80kg he said any harder and the front would wash out too easy when hitting a bump mid corner. i don't really know if he was right but he races bikes as well so i would assume he knows a thing or two.
    The rear is adjustable to some extent but again i have no idea what does what.
  18. just had a look at Zenodamper based at sydney performance motorcycles in north sydney has anyone had any dealings with these guys??
    good/bad/reasonable price??
  19. Dropping the forks through the triple clamp apparently helps. Rear suspension is preload adjustable.

    If i was you, and wanted to get more power out of your bike i would do as follows.
    Rebuild, Get good compression and power
    Expansions chamber + end can rejet. More power, better midrange, more overrev.
    Prob leave it at that, other mods just get complicated
  20. by rebuild do u mean just top end or bottem end as well??
    expansion chamber and end can from jolly moto seem to be the ones everyone goes for i have seen them for about $900 is that a reasonable price?
    what about 34mm carbs i have heard that is what makes the biggest difference of all would that make it any less reliable?