Top 8 Problems with Aprilia RS 125 You Must Know

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The Aprilia RS 125, while a remarkable motorcycle heralded for its performance and design, is not without its share of issues. 

Aprilia RS125 Problems

Navigating these problems can be a bit daunting, especially for new owners. So, in this article, I’ll show you the Aprilia RS125 common problems and offer their solutions.

Let’s begin!

Aprilia RS125 Problems

Aprilia RS125’s common problems are battery issues, gear oil issues, air box, exhaust concerns, rev limit issues, side stand cut-out switch, fuel quality, and storage problems.

1. Battery Issues

Often, these issues can be traced back to the motorcycle being left unused for extended periods. 

During such times, the battery continues to slowly discharge, leading to a state of complete drain. 

When in this state, although recharging might seem to temporarily solve the problem, the battery’s ability to hold a charge diminishes significantly. 

This means that despite a full charge, the battery will drain faster than normal, which affects the motorcycle’s performance. 

2. Gear Oil and Clutch Issues

The first sign of trouble usually is the appearance of a jet-black color in the gear oil, a clear indication that it requires a change. 

Post-oil change, it’s not uncommon to encounter a somewhat stiff gear change and trouble finding neutral. 

Moreover, there might be some play in the clutch lever, which shouldn’t be ignored.

Addressing these issues will improve your bike’s performance. If there is difficulty in shifting gears, you should re-adjust your clutch free play. 

This can be done by loosening the lock nut on the clutch lever and then turning the adjustment nut to either increase or decrease the free play, based on your preference. 

Once done, ensure to tighten the lock nut back into position. For the stiff gears, try using a different brand or viscosity of gear oil, as sometimes the bike might respond better to a particular type of gear oil.

3. Air Box and Exhaust Concerns

Some owners have also shown the air box and exhaust-related concerns. It can be indicated by a strong petrol smell from the exhaust, an unblocked snorkel in your air box could be the culprit.

Originally, this snorkel was blocked to restrict the bike, but unblocking it can cause an overly rich fuel mixture.

In such a case, you can perform a carburetor adjustment to lean out the fuel mixture. 

Start by slowly turning the fuel screw inwards, or clockwise, until the engine starts to slow down. 

Then, turn it outwards, or counter-clockwise, until the engine idles at its fastest. Finally, turn it back inwards to find the point where the engine runs the smoothest.

If the problem persists after attempting to adjust the fuel mixture, you may want to consider replacing the main jet in the carburetor. 

A smaller main jet will deliver less fuel, potentially resolving the issue of the bike running rich. 

Lastly, to ensure your bike has a fresh and clean supply of air, regular maintenance of the air box is critical.

4. Idle and Rev Limit Issues

Aprilia RS125 owners might occasionally experience issues with idling at around 1000 RPM and difficulties revving past 10,000 RPM. 

These problems could be due to several factors, one of which is an improperly adjusted idle screw.

The idle screw controls the engine’s idle speed when the throttle is completely closed. If it’s not set correctly, the bike can struggle to maintain an idle speed. 

You can alleviate this problem by slowly adjusting the idle screw, preferably while the engine is at operating temperature. 

Turn it clockwise to increase the idle speed and counter-clockwise to decrease it. A second common issue could be damage to the throttle slide. 

The throttle slide is an integral part of the carburetor that controls the flow of air and fuel into the engine. 

If it’s damaged or worn, it could disrupt the balance of air and fuel, preventing the engine from reaching higher RPMs. 

Inspect the throttle slide for any signs of wear or damage. If confirmed, you might need to replace it. 

5. Side Stand Cut Out Switch

The side stand cut-out switch can occasionally be the culprit behind your Aprilia RS125’s engine cutting out when engaging first gear. 

This safety feature is designed to prevent you from driving away with the side stand down, but a malfunctioning switch might mistakenly believe the side stand is still extended even when it’s not.

Here is a straightforward solution you can try:

First, locate the side stand cut-out switch; it’s usually attached to the side stand itself. Check it for any signs of damage or wear. 

If the switch appears physically intact, try spraying some electrical contact cleaner into the switch. 

This can help clean off any grime or dust that’s interfering with its function. If this doesn’t solve the problem, consider bypassing the switch. 

Do this by disconnecting the two wires leading to the switch and joining them together. This will trick the bike into thinking the stand is always up. 

However, remember that now the bike won’t cut off if you do leave the side stand down, so always double-check before you ride.

6. Top End Rebuild Considerations

This problem often arises due to the high-performance nature of the bike. The RS125, while a terrific machine, tends to be ridden hard, which can lead to accelerated wear and tear on the engine’s top end.

The top-end rebuild process involves replacing the piston, piston rings, and cylinder. It may also include refurbishing or replacing the cylinder head if it’s been damaged. 

One indication that a top-end rebuild may be necessary is decreasing performance or an increase in noise from the engine.

Performing a top-end rebuild requires a good understanding of your Aprilia’s engine and the right tools. 

Begin by removing the fuel tank and the radiator to access the engine. Once this is done, you can remove the cylinder head and the piston. 

After replacing the worn-out components, you can reassemble the engine in reverse order. 

7. Fuel Quality and Storage

These problems typically arise when the bike is not used for an extended period of time. 

During this period, the gasoline can deteriorate and form a gummy residue, commonly referred to as “varnish”. This can clog the carburetor, leading to poor engine performance.

The problem is exacerbated by the ethanol content in most gasoline, which can attract moisture over time. Moisture in the fuel system can lead to corrosion and other problems. 

Furthermore, ethanol can dissolve certain types of rubber and plastic, which can lead to additional mechanical issues.

To resolve this issue, you should replace fuel if the bike is to be stored for more than a couple of months. 

You can do this by disconnecting the fuel line from the carburetor and allowing the fuel to drain into a suitable container. Reconnect the fuel line afterward.

8. Engine and Dash Issues

The issue often stems from the bike’s high-performance 2-stroke engine, which, while offering impressive power output, can be prone to wear and tear. 

One symptom of this issue is a significant decrease in engine efficiency or a sudden drop in power. 

To resolve this, you should regularly maintain the engine components. Specifically, piston rings should be replaced every 6,000 miles. 

At the 12,000-mile mark, it is recommended to replace both the piston and the rings in high-performance 2-stroke engines due to wear and tear.

You should also use a high-quality 2-stroke oil for the Aprilia RS125. It improves engine lubrication, reducing friction and enhancing performance.

Dash issues in bikes are commonly caused by electrical faults in the wiring system. 

Regular inspections of the wiring, connectors, and fuses can help detect and fix loose connections or corroded elements.

Aprilia RS125 Fuel Consumption

The fuel consumption of the Aprilia RS125 can vary based on the model and riding conditions. 

The full-power RS model with a 28mm carb has an estimated fuel economy of around 45 mpg, giving over 100 miles per tank. 

An early model with a 34mm carb can achieve an average of 55 mpg, and up to 74.5 mpg when driven conservatively during fuel strikes. 

However, modifications such as a bigger carb, straight-through exhaust, and Pipercross air filter can result in fuel consumption of 36 mpg under constant wide-open throttle conditions.

Aprilia RS125 Technical Specifications

Specification CategorySpecification Details
General Information
ModelAprilia RS 125
Start Year2020
Dimensions, Aerodynamics, and Weight
Frame TypeSloping twin-spar frame in thin wall box section cast aluminium, with reinforcement cross-ribbing
Wheelbase1,353 mm (53.3 inches)
Length1,968 mm (77.5 inches)
Width760 mm (29.9 inches)
Height1,135 mm (44.7 inches)
Seat Height820 mm (32.3 inches)
Front Tyres – Rims Dimensions100/80-R17
Rear Tyres – Rims Dimensions130/70-R17
Front BrakesSingle disc
Rear BrakesSingle disc
Front Brakes Dimensions300 mm (11.8 inches)
Rear Brakes Dimensions218 mm (8.6 inches)
Fuel Tank Capacity14.50 litres (3.83 gallons)
Engine and Transmission
Engine TypeSingle cylinder, four-stroke
Engine DetailsRead valve intake
Fuel SystemCarburettor. Magneti Marelli M3G ø 32mm ECU
Engine Size124.20 ccm (7.58 cubic inches)
Bore x Stroke58.0 x 47.0 mm (2.3 x 1.9 inches)
Compression Ratio12.5:1
Maximum Power28.16 HP (20.6 kW)
Cooling SystemLiquid
Transmission Type, Final Drive RatioChain
Clutch TypeMulti-plate in oil bath
EmissionsEuro 4
Electrical Systems, Ignition, and Equipment
Ignition TypeElectronic with CDI capacity discharge
Starter TypeElectric

You can also check out the problems with Aprilia Shiver 750, Aprilia Shiver 900, Aprilia Tuono V4, Tuareg 660, Scarabeo 500, Scarabeo 200, Pegaso 650 & Aprilia RS 660

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