Ok guys. Im really sick of the misinformation going around on this forum.
There are 3 types of derbi moped motors made.
Piston port engines
cylinder inducted
stroke: 43mm
bore: 38mm
displacement: 48.7cc
compression 8.5:1
direction of rotation: counter clockwise facing magneto
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
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
before some of you get all uppity, I copied that out of the repair manuals for all 3 motors except the pyramid reed which is off an old promotional ad I have.