"86 and 87 sle should be a flat reed engine, the flat reed engine came into play in 86, you can tell if it has a steel rear swingarm on a variant step thru, it is a flat reed, if its alloy, its piston port or pyramid
the 81 sle was pyramid reed, derbi rd’s were pyramid reed, derbi diablos are piston port, derbi lagunas are also piston port, the derbi ds50 scooter is flat reed'
quote by well known derbi conoseiour
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