Engine Intake Info

  • 'some late 85's, 86's and '87 SLE should be a flat reed engine (the flat reed engine came into play in late '85)
    • If the engine and swing arm move with the suspension, it is a flat reed
    • If the motor is rigidly attached to the frame it's piston port or pyramid reed
  • the 81 SLE was pyramid reed
  • Derbi RD's were pyramid reed
  • Derbi Diablos and Lagunas piston port
  • the Derbi DS50 scooter is flat reed

Technical Specs

Piston port engines

  • cylinder inducted
  • stroke: 43mm
  • bore: 38mm
  • displacement: 48.7cc
  • compression 8.5:1
  • direction of rotation: counter clockwise facing magneto

Download the repair manual for Derbi piston port motors here.

Pyramid reed engines

  • Pyramid 3-reed valve, Crankcase mounted
  • stroke: 43mm
  • bore: 38mm
  • displacement: 48.6cc
  • compression 8.5:1
  • direction of rotation: counter clockwise facing magneto.

Flat reed engines

flat reed engines were completely redesigned from the earlier piston port/pyramid reed engines. They are not directly swappable to older bikes. Flat reed engines come stock with a 6 roller variator which accepts standard 16x3 variator weights. Flat reed motors also use cast aluminum rear pulleys instead of the stamped steel version on older engines.

  • Crankcase 2-reed valve induction with triple transfer port distribution
  • stroke: 40mm
  • bore: 39.87mm
  • displacement: 49cc
  • compression: 10:1
  • direction of rotation: clockwise facing magneto.
  • Max engine RPM: 6500 (stock configuration)
  • Flywheel and Clutch bell nuts are reverse thread

See a PDF file of the flat reed engine repair manual here.

Make a Water-Cooled Derbi

Please see this discussion from the forums.

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