need speed

Discussion in 'Photos & Bicycle Builds' started by rj1967, May 14, 2015.

  1. rj1967

    rj1967 Member

    Can anyone reccomend an idea to get a little more speed out of my elcheapo 80cc? It goes about 30mph as is. Would like to hit 40 at least. Also best site for replacement parts? Thanks.

  2. dougsr.874

    dougsr.874 Active Member

    Buy a motorcycle
    The_Aleman and Timbone like this.
  3. mikemarley

    mikemarley Member

    A good place to start is a speed carb, its 20 bucks nd if you want a little more top end try and find a banna expansion chamber. Bikeberry is always cheap nd their customer support is awesome, try them
  4. mikemarley

    mikemarley Member

    You really need to do alot to these engines to make them breath fire, ive got a racing 66cc motor and it goes mid 50s but ive also got about 1000$ invested in just in the engine internals, carb, and exhaust. I couldve got a motorcycle but didnt haha i love 2 strokes
  5. mikemarley

    mikemarley Member

    And p.s. its a 66cc the chinese call them 80s as a marketing ploy, there is only a 47mm piston and i forget the bore, i think its 38mm if i remember.
    but anyways multiply the 2 and you get 66cc not 80 as the chinese claim
  6. jaguar

    jaguar Well-Known Member

    click on my signature link to find out about all the best mods you can do to it
  7. rj1967

    rj1967 Member

    Thanks guys. I'm thinking expansion chamber is my best bet.
  8. mcchicken messiah

    mcchicken messiah New Member

    It really depends on if you've done anything to your "el-cheapo" so far.

    If you haven't done anything... you can get a better carb, expansion chamber exhaust, replace your intake and exhaust manifolds and re-bore your reciprocal jug ports to match,
    replace your jug head with a high compression milled or cast cylinder head (crmachine or puch are good options), get your crankshaft balanced, replace your billet rod, etc, etc
    (Yes, there is actually more, much more)

    Now, I haven't owned any of these, BUT, if you really want to squeeze out everything you can from these, expect to pay for it unless you can fabricate / modify some of the parts yourself...

    That being said, there are TONS of parts out there and documentation on the aforementioned.

    Alternatively, you could purchase a different motor....

    Maybe the best question is, what specifically are you trying to accomplish, and how much are you willing to spend to achieve that?
  9. KCvale

    KCvale Motorized Bicycle Vendor has a good expansion chamber and get an NGK 5944 (BPR7HIX) Itidium spark plug while you are there too, the 2 will wake your engine up for ~5 more MPH.
  10. Leroybrown420

    Leroybrown420 Member

    I've had great luck port matching the muffler and intake, trimming the piston skirt, upgrading ignition (plug & wire), hi flow air filter and jetting the carb. Remember, 40mph if really fast for a bike. The faster you go the faster things brake and the more maintenance will be required. You can always buy a Chinese 150cc scooter for a few hundred bucks, they cruise 40-50mph all day long.
  11. butre

    butre Well-Known Member

    porting is the only way to get an extra 10 mph out of it
  12. The_Aleman

    The_Aleman Active Member

    If you're really intent on getting more speed out of your chinagirl, the single best way to go about it is to put on a smaller rear sprocket.

    Using a standard kit 44T as an example, the chinagirl will be @ 6K RPM @ 26MPH with a 26" rear wheel. 30MPH is 7K RPM.
    Every 1T smaller you go on the rear sprocket will get you about 1 more MPH at same RPM.

    Therefore, if you used, say, a 36T sprocket, you'd get 34MPH @ 6K, 38MPH @ 7K.
  13. KCvale

    KCvale Motorized Bicycle Vendor

    Gearing of course, gears change everything, but you still need the engine beef to push it.

    Once you hit ~32mph wind resistance is like ~80% of the battle to gain more speed.
    You need engine beef to overpower wind resistance if you want to sit up, or get aerodynamic with cowlings and low tucked in riding posture if you want to go really fast, but please just keep in mind you need to improve your brakes as you improve your top speed.
  14. The_Aleman

    The_Aleman Active Member

    I had no problem hitting 38-42MPH with a stock 66CC and a 34T rear sprocket 8 years ago. I'm 6'4" 230 and ride bagged bikes.

    Of course, the only reason I changed my sprocket was so I could cruise at 30MPH without spinning my engine over 6K.

    Chinagirls make pretty good torque between 3-5K RPM, even with a stock pipe.