BUYING A USED APRILIA RS 125 buyers guide RS125

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Aprilia RS125: Used Buyer’s Inspection & Reliability Guide

Buying a used RS125 is a high-risk endeavor because these 2-strokes are often neglected by young riders. This guide highlights the "must-check" items to avoid a mechanical debt trap:

• The Top-End History: Ask when the piston was last changed. If it has done more than 6,000–8,000 miles, factor the cost of a rebuild into the price. A "top-end seizure" is the most common reason for a cheap sale.

• The "Nylon" Gears: On the Rotax 122 engine, the balance shaft gears are plastic. If they haven't been replaced in 15,000 miles, they can melt, causing the engine to vibrate until it destroys the main bearings.

• The RAVE Valve Test: During the test ride, the bike should "kick" at 8,000 RPM. If it feels flat, the power valve is either carbon-locked, the solenoid is dead, or the CDI is restricted.

• Cosmetic Red Flags: Look for "rash" on the bar ends and footpegs. These bikes are frequently crashed; check if the fairings are genuine or cheap, brittle aftermarket replacements.

• The Gearbox: Ensure it doesn't "pop out" of second gear under hard acceleration—a sign of worn selector forks from clutchless shifting.

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Purchasing an APRILA  RS125.

Whilst buying an RS125 you have to be aware of the following:

They are not unreliable bikes, forget all the stories you  heard. These are solid bikes. They are one of the most highly tuned road bikes, and as such demand high maintenance, high quality oils and sensible riding procedures.

there is no bad rs125 just badly maintained ones

Yamaha R1  150 hp per litre , RS125 produces a massive 250 hp per litre!!!!!!!!!!!

this power demands race quality maintenance  , avoid any bike that looks uncared for unless your willing to spend time on getting it back to tip top condition(which can be fun but expensive) , having said this most used rs125 bikes will need a good overhaul prior to riding, me i personally rebuild every bikes engine and fully look the bike over , i then know i am riding a good bike  .

when first looking at a bike, check its mileage like any bike, check to see of its stolen recovered HPI clear or a previous insurance write off these are important and must be done prior to buying i have lost count of how many people have been done this way .
if the buyer has no V5 or documentation then do not buy it , i have known people get in serious trouble going to court over stolen engines in bikes they have bought.

check the overall condition of bike in particular the braking systems , chain and cogs inside fuel tank (rust if metal ),does it start well from cold and sound good but like i say expect to need to rebuild an engine soon , its just needed on a 125 2t so if this scares you or you cant afford it you might be best of with 4t.

Be aware in the RS125 manual, it suggests you check your piston rings at 9,000km and change the piston and rings at 16,000km. So if its past these mileages ensure that this has been done by the previous owner but most bikes i see advertised say fully rebuilt engine , this would worry me more i prefer to do my own engine builds i know then the best parts are fitted and fitted correct .

an engine compression test is a good test to see if the engines piston and rings are good heres a video of how to do a compression test ensure you throttle is in wide open position

if the bike has more mile say around 20/30000 for a well looked after rs125 then a complete engine rebuild should be done this will include barrel , piston, conrod , bearings etc etc.

can you afford to rebuild the complete engine , can you do this work yourself if not 2t rs125s might not be for you 


If you are purchasing a full power bike it will have a power valve in it. This is a mechanism that makes the exhaust outlet wider and narrower as the revs increase and decrease giving the best performance. 

this can also mean that the bikes engine has extra wear and tear due to more power and will mean that its not suitable for a 17yo riders licence.

rave unit aprilia rs125 

The earlier bikes had a 34mm carb on them, but they were replaced with 28mm carbs. This means the newer bikes do not get as much mid range power. So if your test riding different years beware of this. You can always get hold of a 34mm carb and manifold inlet and put this straight on to the bike without any extra parts to get that performance.

aprilia rs125 34mm carb

Mods. If you get to an RS and its not standard make sure its been set up correctly. If you notice its got a fancy air filter on there make sure it has been jetted accordingly by the owner. If not the bike could be running lean! 

This is very bad, meaning a seizure is very likely when a bike is running lean. If you notice a different exhaust and expansion chamber, make sure it has been jetted. As if it originally had a standard expansion chamber with a CAT in it, it will be running far too rich.

a good rs125 will have been looked after properly. E.g. chain and sprockets are in decent condition, just the general condition of the bike , where it was stored etc etc .

BUY the ultimate Aprilia RS 125 workshop manual bundle HERE