what are some of the best mods to do?

Discussion in 'Motorized Bicycle General Discussion' started by iungerich1, Nov 27, 2013.

  1. iungerich1

    iungerich1 New Member

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    Ok so i just got my bike built a week ago and its kinda lacking in the speed department. i was wondering what are some of the best mods to do to it to maybe help improve the speed? i was thinking about getting a new carb ( as i am running the stock one now and dont really like it) which do you recommend?
    should i get a new air filter? which do you recommend?

    thanks for the help
    -iungerich1
    :-||
     
  2. MotorBicycleRacing

    MotorBicycleRacing Active Member

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    Welcome to the forum. :)
    I assume you have a China girl of some kind?

    There are a few stock carbs so which one do you have? What don't you like about it?

    Have many more questions than answers seeing who knows what your build is?

    Posting a pic would help.

    Do you tackle hills where you ride and how are you proportioned? :D

    Changing the rear sprocket is an easy and effective way to speed.

    How fast are you going now?
     
  3. 2door

    2door Moderator
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    It would help if we knew what engine and carburetor you have. 2 stroke or 4?

    If a Chinese 2 stroke, in-frame kit then my suggestion first of all would be to give it some time. They don't break in over night. It will take a minimum of 200, preferably 300 miles to seat the rings and get the compression up to where it's supposed to be. They are like a good wine; they get better with age (miles).

    As far as carburetion, again if we're talking about a Chinese 2 stroke, what carb did you get? The CNS is notorious for being hard to tune but those who have mastered it swear by it. The venerable NT is hard to beat on an engine in a stock configuration.

    Again, if a 2 stroke, an expansion chamber exhaust will give you a noticable performance increase but don't expect motorcycle performance. It is a motorized bicycle and 25 to 30mph is about normal. How fast do expect to ride?

    Tom
     
  4. maniac57

    maniac57 Old, Fat, and still faster than you

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    Wait until you have a few tanks of fuel through it, then get a decent tuned pipe and a smaller rear sprocket. I run a 36 tooth and pipe and am quite happy with the better cruising speed and lower revs.
    Unless you live in a hilly area, you will love the improvement.
    Be aware you will lose acceleration on the low end to gain top speed. The pipe should help make it up by improving torque.
    If you want the best of both worlds and have the means, get a jackshaft shifter kit.
    In my opinion, a bigger carb on the stock engine is a waste of money. The stock nt works quite well and is easy to tune. Carb upgrades are down the list below porting work.
    Spend your cash where it will actually make your bike faster.
     
  5. iungerich1

    iungerich1 New Member

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    %#2$$%@$!#%$^$#
     
    #5 iungerich1, Nov 27, 2013
    Last edited: Nov 28, 2013
  6. iungerich1

    iungerich1 New Member

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    if china girl means cheep china kit i bought off ebay then yes i have one of those :)
     

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  7. MotorBicycleRacing

    MotorBicycleRacing Active Member

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    So how fast are you going?

    You have an NT carb, nothing wrong with it.
    Try moving the clip on the needle up one notch to lean it out a bit.
     
  8. rogergendron1

    rogergendron1 New Member

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    the best mods are as follows in this order
    0 tune carb
    1 port and polish and port match
    2 deck your head or high comp head
    3 tunned x chamber power band or strait pipe for WOT racing
    4 larger carb 16mm dellorto phbg or sha 16.16mm or mikuni vm18mm or
    5 piston mods IE... grind ramps, cut skirt, and lighter wrist pin and bearings
    6 reed valve intake arrow or rock solid

    the grubee gt5 on the last pic has the mods listed. high comp head, port and polish with extra 3rd transfer port ground, tunned x chamber exhaust from arrow, arrows reed valve intake, delorto 16.16mm sha carb, and a modified piston ie .. ramps cut to modify transfer port timing and exhaust duration, and better bearings.

    sells for like 600$ but can be built for less than half that if you have the mechanical know how
     

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    #8 rogergendron1, Nov 28, 2013
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  9. rogergendron1

    rogergendron1 New Member

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    like maniac57 said gearing plays a huge role also !!!!!!!111

    the stock 44 rear is meant to limmit speed but i like the added torque it provides, going down to a 40t rear will net you around 5mph top speed and lower your revs without sacraficing power to any noticable extent, 36t will net you around 10mph top speed at the cost of torque.

    there is a simple stock exhaust mod linked in my sig if you know how to use a dremal and can weld or know someone who can weld for u. you will free up your motors breathability and gain a noticable amount of power everwhere at the cost of more noise and a lil work.

    i also have some top end mods listed if your interested in that.

    if you want to mod on the cheap than do a good moderate port and port matching, grind piston ramps, and mod your stock exhaust all for free if u own a dremal

    get a puch 70 hi hi head, 40$ and a dax rt carb 30$

    tottal around 80 - 90$ for a well done street ripper !
     

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    #9 rogergendron1, Nov 28, 2013
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  10. MotorBicycleRacing

    MotorBicycleRacing Active Member

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    $600?
    The Arrow Motorized Cycles Street Racer sells for only $499

    Has an,
    $85 CR Machine billet head.
    $55 Torquer II pipe
    $85 reed block
    $50 Carb
    $65 Pro reed ported cylinder
    $90 PRO assembled GT 5 SkyHawk motor

    The lower end bearings are not changed because there is nothing wrong with the stock ones which I think are Japanese in the Skyhawk.

    I don't think there are any piston ramps on the Arrow Street Motor.
    It does have good port timing though. I will ask Dave.

    The best mod bang for the buck is an expansion chamber.

    What do you mean by a straight pipe for a 2 stroke?
    Straight pipes sort of work on 4 strokes.

    The Rock Solid reed valve is a joke as it is sized for a 30 cc motor not these 66cc to 69cc motors
     
    #10 MotorBicycleRacing, Nov 28, 2013
    Last edited: Nov 28, 2013
  11. rogergendron1

    rogergendron1 New Member

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    yeh 500 plus shipping ? well i thought it was 600 for some reason IDK mabey i was thinking of the balanced one lol

    i my self am in the market for a dellorto carb but am wondering why most all places seem to have the 14 or 15mm sha or clone and do not carry the real 16.16mm ? 16 -18mm seems like the sweet spot for the 70cc motor, why does everyone go for 15mm carbs ? i would rather have the 16mm phgb or 16.16mm sha or even a 18mm phgb or 18mm mikuni so why are all the so called preformance options 15mm same as stock ? i have a 21 mm i know for a fact i could make work but would only be good for WOT racing 18 seems like a good inbetween

    and motorbicycleracing is correct a x chamber will give you the most for your money, its something you can feel and substantiate right on the first ride, however i like to do that after i get the compression ratio i want and port it the way i want and get the top end modded and lightend then i make the exhaust tunned to the motor, this way i dont have to keep chopping it up and changing header lengths and sutch to keep retuning it after every major mod lol
     
    #11 rogergendron1, Nov 28, 2013
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  12. MotorBicycleRacing

    MotorBicycleRacing Active Member

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    44 tooth at 7000 = 30 mph
    40 tooth at 7000 = 33 mph = 3 mph difference.
    36 tooth at 7000 = 36.7 mph = 6.7 mph difference
     
  13. rogergendron1

    rogergendron1 New Member

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    i dont know if this is considered a mod or not but... find the cleanest fuel you can preferably ethanol free and run that all the time mixed with a good synthetic oil like opti 2 or lucas oil or pro mix at 40 to 1 or 32 to 1 start around there and find the mix ratio your bike likes and stick with that fuel and mix ratio your bike will love you

    my grubee gt5 likes true fuel 40:1 or pro mix and 93 oct 40:1 with a good dash of lucas oil upper cylinder lube, its jetted for that and runs great any leaner on the oil and she looses preformance richer on the oil and there is dripping from the pipe
     
    #13 rogergendron1, Nov 28, 2013
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  14. rogergendron1

    rogergendron1 New Member

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    thats exactly correct, i was tossing out rough estamates bassed on the pluss one minus one tooth = plus one minus one mph 5mph or 3 mph whatever close enough lol

    the 40 t and 41 tooth seems to be where its at though and they should come stock with all kits

    it should aslo be known that the ability to get to a certain rpm my change based on gear ratio also ! what good would a 36t at 7,000 rpms do if your motor cant spin at 7,000 rpms under the load of the smaller gear and rider wieght ? lets say it tops out at 5,700 due to load ? when a lil larger gear may ease the load and allow higher rev's say 7,000 with a 41 or 40

    gearing and a free flowing exhaust are the most important factors in making a stock motor GO

    i am a rambling maniac lol i know how to preformance tune a motor but fall short on explanations and teachings, listen to folks like motorbicycleraceing and mapbike and maniac57 they know there stuff
     
    #14 rogergendron1, Nov 28, 2013
    Last edited: Nov 28, 2013
  15. MotorBicycleRacing

    MotorBicycleRacing Active Member

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    Hey, the advice we are giving is directed towards a novice who
    just put a motor on a bike.
    He ain't going to be hacking up motors like you. :D
     
  16. MotorBicycleRacing

    MotorBicycleRacing Active Member

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    The kit I sell does come stock with a 41 tooth sprocket. :)

    Exactly! The kit I sell does come with a 41 tooth dished sprocket. :)
     
  17. rogergendron1

    rogergendron1 New Member

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    The goal of a tuned straight pipe in this application is to use the reflected negative pressure waves from the open end of the pipe to help draw out the exhaust gases. By selecting the appropriate length of the pipe, the reflected rarefaction wave arrives at the exhaust port just as the transfer port opens thus assisting the flow of fresh mixture into the cylinder, and exhaust gases out of the cylinder. The figure below illustrates this action. In the figure, even though the piston has reached bottom dead center (BDC), fresh mixture continues to enter the cylinder because the rarefaction wave causes P2 to be smaller than P1. A key point to note is that the velocity with which the pressure and rarefaction waves travel down and up the exhaust pipe is for the most part independent of the engine operating frequency (RPM). Due to this fact, the conclusion must be made that for a given pipe length there is an optimal RPM for which the waves will arrive producing the greatest benefit for the breathing of the engine. At this optimal RPM, the engine breathes significantly better and hence produces a noticeable increase in output power. This effect is quantified by calculating the ratio of fresh mixture to exhaust gases within the cylinder as the compression stage begins at EPC. If the rarefaction wave is very large, it is possible that fresh mixture is pulled into the exhaust pipe while both transfer and exhaust ports are open. This phenomenon is known as short circuiting the engine and produces undesired effects such as a decrease in fuel economy and an increase in release of volatile organic compounds. These negative effects can be mitigated by designing the exhaust system such that either no fresh mixture is pulled into the exhaust pipe (i.e. perfectly tuned straight pipe) or further utilizing the exhaust pressure wave to inhibit short circuiting. For performance two-stroke engines, the second solution is most often employed by means of a tuned exhaust pipe known as a tune pipe.

    strait pipes work on 2 strokes as long as they are the correct length ! they are most effective at high rpm riding like WOT aplications. the length is made so the wave exits the end of the pipe at just the right time to create a slight suction to aid with pulling in the intake charge . though not as good as a tunned x chamber its cheap and WORKS !!!! the highest top speed i have achieved on my bike was with a tunned striat pipe !

    of course there is a dissadvantage also...
    Of course those waves don't radiate in all directions since there's a pipe attached to the port. Early two strokes had straight pipes, a simple length of tube attached to the exhaust port. This created a single "negative" wave that helped suck spent exhaust gases out of the cylinder. And since sound waves that start at the end of the pipe travel to the other end at the speed of sound, there was only a small rpm range where the negative wave's return would reach the exhaust port at a useful time: At too low of an rpm, the wave would return too soon, bouncing back out the port. And at too high of an rpm, the piston would have traveled up the cylinder far enough to close the exhaust port, again doing no good.

    Indeed, the only advantage to this crude pipe system was that it was easy to tune: You simply started with a long pipe and started cutting it off until the motor ran best at the engine speed you wanted.


    its the easyest damn mod to do a 1in aluminum strait pipe !!! make it too long and then cut 1in at a time till you get it to the driving rpm you use most and you will always have power in that rpm range. want to change it ? add another inch or take off another inch ! soo easy but it only gives a small but powerfull power band. a tunned x chamber will definatly give you a broader band but cost a lot more and is more difficult to make . try it out some time if you wan to play aroung with small but powerfull rpm ranges !

    i am a cheap baStrd so i make strait pipes for my motors at the given rpm i ride that bike at most and so far i have had great results though i know not as good of results as if i had a propper tuuned x chamber but my girly wont weld me any more complicated stupid bike parts lol her words... at least i got 1 good tunned pipe out of her lollollol
     

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  18. rogergendron1

    rogergendron1 New Member

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    lol i ride em then grind em lol the grind em part is me experimenting with the old parts .....

    i say tunned pipe (x chamber)
    41 or 40 t rear
    rt carb
    cheap high comp head

    with that you wont believe its the same motor .wee.
     
  19. Danschutz

    Danschutz New Member

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    I called him the other day and he highly suggested to not "notch" the piston on that motor. His motors are tuned for maximum power and it would hurt the timing.

    Im still deciding if I want one of Daves "Big Block" top ends.
    Neil, you have any thoughts on the Big Block Reed cylinder?

    Oh and Happy Thanksgiving : )

    Dan.
     
  20. rogergendron1

    rogergendron1 New Member

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    i bet it would hurt the timing !!! those arrow jugs ports are tunned perfect , on a stock jug however ..... those ramps and a lil skirt cutting brings the timming to where it needs to be. a stock jug has to much deck hight and the port timing is to high up the cyclinder ramping the piston adds needed duration to the exhuast and transfers same as if you raised and widend them and trimming the skirt adds duration to the intake same as lowering the port hight.
     

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