Engine Trouble Help with bike build

Discussion in '2-Stroke Engines' started by treys2k, Jul 2, 2015.

  1. treys2k

    treys2k New Member

    Hello, im new here so let me knoe if this is the right place to post. So I have a 25cc weed wacker engine Im putting on a 20in bmx bike. Instead of friction drive I actually attached a sprocket to the drive shaft. The motor is bolted into the frame. The pull start from the motor was damaged and removed. My question is if I run a chain right to the back wheel off the drive shaft mounted sproket with no pull start how could I start the bike?? Thanks for any help!

  2. crassius

    crassius Well-Known Member

    without a clutch to disengage the motor, I'd think the question would become "how to stop the bike?"
  3. KCvale

    KCvale Motorized Bicycle Vendor

    If it has no clutch so just pedal it, it will start, but die every time you come to a stop.
    If it has a centrifugal clutch you can stop with the engine running, but you can't start it by pedal bump starting.

    This is why all MB 2-stroke engines have a manual clutch.
    You pedal them up to start, and hold the clutch in when stopped so the engine don't die.

    You can get a new pull start but it's a 25cc engine meant for high RPM and minimal load (it just spins string), far from ideal to power you on bicycle even if it was free.