i can tell you that rs 125's suffer from a few problems,firstly the powervalve hits the piston when it wears and the barrel is nickel plated so it not cheap when it does it,the balance weight gears are made of nylon and they break which makes the engines shake,the dellorto carbs are crap and they have a poor tickover screw arrangment basically the tickover screw pushes against a slanted part at the bottom of the throttle slide like most singles do but the dellorto ones have a very short ramp that the screw touches and it wears out and then you cant get the bike to tickover.its not uncommon for the big end bearing to collapse either i have rebulit loads of these crankshafts (and engines)by fitting new con rod kits.And lastly the head gaskets and water jacket gaskets are rubber rings and they often leak.these are good bikes but they need alot of tlc to keep them running right the earlier ones had a rotax 123 angine and the later ones use a rotax 122 engine its stamped on top of the engine behind the barrel.
adam bike doctor, May 2010
