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

Derbi mopeds came with three engine sets.

1 - Piston port , same stroke as Puch. With modifications you can out a puch cylinder on a derbi piston port bike. Super easy swap back and forth. If you are somewhat clever.

2 Pyramid Reed Derbi. Same stroke as piston port but with case inducted reeds. Not easy to swap things around, because you have case induction. So technically you could run puch kit if you sealed up the case induction.

3 Flat reed. Basically the last edition of derbi. Much like a bunch of scooters. Very similar stroke to hobbits and minarelli horizontal scooter kits. Lot's of blasty options but not puch kits. These have DISsimilar bore and stoke to the previous two DERBI motors.

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 reed engines share the same internals as piston port motors except they are case inducted.

  • 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 16x13 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.

Derbi Laguna Sport

Derbi began importing mopeds to the United States in 1978, After 2 years of this they began to market a bike specific to the US market. The Derbi Laguna Sport most likely recieved its name from the Derbi moped headquarters in the United States at the time located in Laguna Hills, CA. The Laguna Sport was designed after its Spanish counterpart the Sport Coppa (a 5-speed moped Derbi created in response to the Puch Monza). The Laguna Sport was sold thru 1980 and early 1981 and discontinued afterwards, There is no exact tally of how many went into production, as they were not individualy numbered. Derbi had 2 other similar models; The C-5 Diablo and RD-50 which were more oriented for motocross aplications.

  • Lost Laguna/C-5 gas caps can be replaced with a 1 hole #8 (41mm x 33mm x 25mm) stopper from any lab store. Just be sure to run tubing from the cap down the frame to keep water and vacuum sealage out!
Derbi Laguna