125cc 2stroke Tuning Guide.

Discussion in 'Scooter Guides' started by MiNoR cOnFuSiOn, Jan 7, 2009.

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  1. MiNoR cOnFuSiOn

    MiNoR cOnFuSiOn Administrator Staff Member

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    125cc 2stroke Tuning Guide


    First things first, you need a good engine, as in no cracks and if you can't fit them yourself good crank bearings/oil seals (water pump where applicable).

    The power listed on this guide is from experience not claims.


    For sheer power for money and driveability the best setup would comprise of:

    Malossi 172cc kit
    Dell'Orto 25mm Carb (best match for the standard reed window anyway although gains and losses are present with any other carb fitted)
    Gear up kit
    Aftermarket Carbon Reeds
    Runner 125 standard exhaust if you have a Typhoon

    This package is really good for your money, it utilizes the stock pipe so it's pretty much stock looking and will still see a reliable 15+bhp in any fitment. It gives for over 75mph true speeds and will start first time every time. It should also last a long time as there's no real strain on the engine.


    Upping the ante a little we can start looking at utilizing the transmission for best performance, also how to shift the power band of the engine to a taller peakier curve, power doesn't always make for a faster bike.

    Next few things on the list would be:

    Piaggio 180cc variator (Malossi MHR if you're looking to take things further)
    Aftermarket Exhaust (matched stub goes without saying but is ALWAYS forgotten by amateurs)
    Aftermarket Stronger Clutch Springs
    Malossi straight inlet manifold
    Stronger Aftermarket Reeds
    Malossi CDI swap/similar timing advance

    With the new pipe the engine will produce its power all at once in a certain rev range. This means we set the clutch to bite past the flat power at low revs and drop the roller weight slightly. This setup on top of the previous will see powers of up to 23bhp with correct setup although this is dependent on mainly the exhaust/match of the stub and setup.


    Right then, now we get off the kiddie stuff and get busy with big boy cranks, bigger carbs and touch on porting slightly as well as other ways to gain power from the now "beast" like machine you've been creating...

    I'd personally add to this setup:

    Aftermarket Crank (BGM or Malossi)
    New bearings obviously (although stock fitment bearings are good for 40+bhp and last longer than c4's... Also they rarely rev past 10k)
    Malossi MHR or Polini Evo Reedblock (you can mod the stock to the same level as the Malossi or Polini item)
    Bigger carb

    With this setup on top of the previous 2 you can see 25+bhp but this is a fluke in most cases and will need case work to see the power reliably.


    Aftermarket cranks are basically stronger, better balanced, higher revving, larger by volume version of the stock item with the exception of the big end bearing and different stroke cranks now available. A tried and tested crank good for 30+bhp is the Malossi although there are plenty of cranks out there now, adding a crank to this setup will give some performance increase but nothing really noticeable. It runs a lot smoother, revs better and can rev higher if your setup allows (the Malossi crank is good for 16,000rpm for instance) the webs in the crank are also filled (full circle crank) which means primary crankcase compression is raised. This means more fuel and air is packed into your cylinder, which means bigger bang, which means more power.

    Stroker cranks are another way of playing with power. Basically they work by moving the centre of the big end bearing further out from the centre of the crank. Meaning the piston is moving faster at any given rpm. This gives you more low down power but takes a little messing about with. BGM cranks are pretty much plug and play but to make best of them they need port adjustment as well as matching of the special spacer plate to the barrel. With the 55mm crank there is a 3mm difference in the stroke obviously... Meaning the piston moves up and down by 3mm more. Merely moving the barrel up 1.5mm stops the piston hitting the head but you still have port bottoms that don't meet the top of the piston and aren't open long enough for the stroke. They usually make more torque over hp gains (loose hp in some cases) but torque is single turning force rather than running force. Meaning that acceleration is better, low rev power is up and wheelies are made a lot easier as torque keeps you in the air rather than hp.

    Porting on the other hand is how you're really going to see gains, but most people don't actually know what porting is. Porting by definition is playing with the internal ports of the barrel so anything other than that is considered "flowing" work even though it's offered as port work by everyone who does it. "Porting" a crankcase is basically getting as much flow through an engine (measured in cfm or cubic feet per min) with the minimal amount of material taken out to keep primary compression nice and high. An unported crankcase will flow around 40-60cfm where as a properly flowed case will flow well over 110 cfm. As well the transfer feeds to the barrel are made wider so the barrel is fed through a bottleneck when the gas meets the port. The more you can squeeze a gas before it is compressed by the cylinder, the more power you have. That's how superchargers/turbochargers work. Flowing is a way of boosting the amount of air moved as well as the amount it is compressed before it hits the cylinder. Porting is the timings of the ports inside the cylinder. By timings I mean the degree of rotation the piston reaches before opening/closing the ports. This however has the most effect on performance as a barrel is designed with a port map to suite any need basically. You have to remember people designed these kits to stay cool, return good fuel economy, last as long as possible and not kill you if you sacrifice these points you will always go faster.
     
  2. tip1

    tip1 New Member

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    Many thanks for this mate.
     
  3. nibbles

    nibbles Active Member

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    read this countless times in the past wen i use to read oat for fun lol .but good to refresh ma memory n go back to basics
     
  4. james_typh

    james_typh New Member

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    can some1 tell me what a matched stub is plz
    and where do i get 1 from thnks
    i no its probaly a dum question lol

    (matched stub goes without saying but is ALWAYS forgotten by amateurs)
     
  5. nibbles

    nibbles Active Member

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    if you have the money for this work pm minor confusion hes one of the best
     
  6. james_typh

    james_typh New Member

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    do u no how much it would b
    so when i get the money i will pm him possibly
     
  7. bait

    bait Active Member

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    1,667
    have a look through some other project posts read up abit on it look on the net ect and then decide weather you want to have a go yourself..best way 2 learn im going to have a go at it when i get some money for a nice exhaust looking through the project pages on here is very helpful
     
  8. james_typh

    james_typh New Member

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    right ive just looked through the projects and i cant seem 2 find any thing on matching stubs
     
  9. MiNoR cOnFuSiOn

    MiNoR cOnFuSiOn Administrator Staff Member

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    a stub is poart of your exhaust (removable that bolts to your cylinder) you match thesse to the barrel....
     
  10. james_typh

    james_typh New Member

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    i just locked at fatboy87 project and he is doing 1 so i no vagley what to do
    i think i bolt the stub 2 the bore and just widen the in side out but but do i just go straight in to the bore so its just 1 big circle
     
  11. Dec

    Dec Active Member

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    nothing ugm
    lol

    dont do it
     
  12. bait

    bait Active Member

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    1,667
    ye man u misread what i said simply looking at pics is never gona help you read books, search the net dont do a thing till you fully understand what your doing if you dont understand leave it unless you can afford to cock it up
     
  13. james_typh

    james_typh New Member

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    ok thanks 4 help ill read up before i do any thing
     
  14. MiNoR cOnFuSiOn

    MiNoR cOnFuSiOn Administrator Staff Member

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    BEFOR you just give this a go like alot opf people have done, look for anyone who's try'd this an there engine is ACTUALLY running, more to the poiont running with better power an no probs.. ive seen MANY attewmpts at this sort of work (mostly abortions tbh) and not a SINGE vid of one running...

    its NOT easy, iuts NOT a csase of "just give it a go" and i REALLY wish people wouldent keep advising this.. you wouldent give yourself a tonsilectomey and its a simplke cut (fucking simple by comparesen) yet people are happy to just jump into cutting barrels about

    its 0.1mm tollerance.. 1mm difference ANYWHERE is the difference between getting power and loosing power

    DONT try this yourself. DONT pm me asking for info/pricing if yuou dont have money to have it done, its plain annoying and you wouldent walk in a ferari garage, piss the owner about then say "cheers, when im rich ill come get one" now would ya/
     
  15. greggy50

    greggy50 New Member

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    Would you fit a 172cc kit, gear up, 25mm carb and some carbon reeds as looking at getting them in a couple of months and dont fancy doing it myself and wanted an idea of how much getting them fitted would cost really lol.
     
  16. MiNoR cOnFuSiOn

    MiNoR cOnFuSiOn Administrator Staff Member

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    corse... have to bring the engine/bike to me.. pm for any enquireys on any required work.. just not silly questions :)


    as for the guide, i need to update this really its a few years old, few new parts/methods and i want to get into porting and specific's of what type of port for what kind of engine. (as in when you can get away wiht big power and typical use of said engines)
     
  17. greggy50

    greggy50 New Member

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    Okay I will drop you an email nearer the time as no point me doing really until I have the money as just going to be taking up space on your computer lol:)
     
  18. star-172

    star-172 New Member

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    Like this thread :) Very gd info
     
  19. tip1

    tip1 New Member

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    Great guide Minor, when you get the time i would really appreciate you updating it when you get the chance as i would like to know any new methods etc.

    Many thanks

    Ricky
     
  20. 2wheeler

    2wheeler New Member

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    great guide, helped alot :thumbsup:
     
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