how do i now if my rs 125 needs a rebuild?

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

Take it to the nearest scrap yard.

raymondo
May 2010

Simon,
I started with bikes when I was 16 and got some right dogs.. which cost me a bomb! here is some words of experiance....
hate to say it but why did you buy a bike needing so much work when you dont know what you doing. The reason you got it for £300 is because it will need a strip down and loads of work, they need care and attention these bikes and if not looked after are incredibly unreliable. You coulld buy a nice one for the money you are about to spend, could cost you £1000 to put right.... Sell for £350 get you money back and save for a nice one. Get one with a full service history or at least an owner who knows what he/she is doing.

bb
May 2010