100 MPG Madness: Project Aprilia RS50

The Malossi 80cc big bore kit has much larger transfer and exhaust ports.  AF1 did a mild cleanup on our ports, equalizing their heights, chamfering them and removing flash.  After porting we WPC treated the bore.

These small bikes are made to look like anything from a supermoto killer to a mini MotoGP machine and are marketed to those who think scooters are for sissies.  The Aprilia RS50 and the Derbi GPR were the only ones that made it to the USA and the Derbi doesn’t really have parts support as Derbi went belly up in the American market.  The RS50 is a somewhat rare machine and was sold in the USA for only a few years from 1999-2003.  They are starting to be considered collector's bikes with nice examples now becoming expensive.  At the time when we started this project, it was possible to find cheap ones.

The Malossi piston dwarfs the stocker.  We WPC treated the piston, pin and rings.

The RS50 is no joke; it has extensive aftermarket support in Europe where it is raced.  Many engine kits and peripheral accessories are available for it.  It has a Minarelli AM6 50cc water cooled engine with a six speed transmission.  Way more sophisticated than your typical scooter or moped.  The 50cc AM6 pumps out an amazing 8.4 hp stock which equates to about 7 wheel hp.  The RS50 has a cast aluminum twin spar frame, a monoshock rear suspension and Marzocchi front forks just like a big bike.  Large for its size, hydraulic Grimeca disc brakes grace alloy wheels. In short the RS50 shares more in common with big bikes than scooters and rides and handles much better than a scooter.

You can see the size difference between the bore and the exhaust side ports easily here next to the stock cylinder.  Note that the Malossi cylinder has 3 exhaust ports!  A main one and two auxiliary ports at the sides.

Our example was purchased for $800 from a guy who only put 700 miles on it before crashing.  After crashing he shoved it outside to rot since he was now afraid to ride.  When we bought the bike it was in pretty sad shape.  It was dirty and corroded.  The crash had damaged the bodywork on the left side. The left side bars were bent and the shifter thrashed.  However the bike was complete, it ran well and it was cheap!