The Yamaha MT-03 660, a naked bike known for its distinctive styling and torquey single-cylinder engine, holds a special place in the hearts of many riders. However, like any motorcycle, it's not without its quirks and potential problems. Understanding these common issues, and more importantly, knowing how to address them, can save you time, money, and frustration, ensuring a smoother and more enjoyable riding experience.

The MT-03 660: A Quick Overview

Before diving into the nitty-gritty of potential problems, it's worth remembering what makes the MT-03 660 tick. Powered by a 660cc single-cylinder engine borrowed from the Yamaha XT660, it delivers a punchy, characterful ride. Its upright riding position and minimalist design make it a popular choice for urban riding and shorter trips. But this simplicity and the engine's nature can also contribute to some of the issues we'll explore.

So, What Are the Most Common MT-03 660 Problems?

Let's get straight to the point. While the MT-03 660 is generally reliable, some issues crop up more frequently than others. We'll break them down into categories, offering insights and potential solutions.

1. Fueling Issues: A Temperamental Throttle?

One of the most talked-about issues with the MT-03 660 is its sometimes-temperamental fueling. This can manifest as:

  • Jerky Throttle Response: Especially at low speeds, the throttle can feel snatchy and difficult to modulate smoothly. This is often more pronounced on earlier models.
  • Stalling: The bike might stall unexpectedly, particularly when cold or at idle.
  • Poor Fuel Economy: Some owners report fuel economy that's lower than expected for a single-cylinder engine of this size.

What's Causing It?

Several factors can contribute to these fueling issues:

  • Lean Factory Setting: The MT-03 660, like many motorcycles, was often set up lean from the factory to meet emissions regulations. This can exacerbate throttle snatch and stalling.
  • TPS (Throttle Position Sensor) Issues: A faulty or misadjusted TPS can send incorrect signals to the ECU, leading to fueling problems.
  • Idle Speed Adjustment: An incorrectly set idle speed can cause stalling, especially when the engine is cold.
  • Dirty Injector: A clogged fuel injector can affect the spray pattern and fuel delivery, leading to poor performance.
  • Vacuum Leaks: Air leaks in the intake system can disrupt the air/fuel mixture, causing fueling problems.

How to Fix It?

  • ECU Remap/Fueling Modification: This is often the most effective solution for addressing the lean factory setting. A Power Commander, Dynojet O2 controller, or similar device can be used to adjust the fuel map and smooth out the throttle response. A custom remap on a dyno is ideal for optimal results.
  • TPS Adjustment: The TPS can be adjusted to ensure it's sending the correct signals. A workshop manual will provide the correct procedure.
  • Idle Speed Adjustment: Ensure the idle speed is set to the manufacturer's specification. This is usually done with a screw located on the throttle body.
  • Fuel Injector Cleaning: Consider having the fuel injector professionally cleaned or using a fuel injector cleaner additive in your fuel.
  • Check for Vacuum Leaks: Inspect all vacuum hoses and intake manifold connections for cracks or leaks. Use a spray bottle with soapy water to check for leaks around joints.

2. Electrical Gremlins: Lights Out?

Electrical issues can be frustrating to diagnose, but they're not uncommon on the MT-03 660. Common symptoms include:

  • Battery Drain: The battery drains quickly, especially if the bike is left unused for a period.
  • Charging Problems: The battery doesn't charge properly while riding.
  • Intermittent Electrical Failures: Lights flicker, the instrument panel malfunctions, or the engine cuts out intermittently.

What's Causing It?

  • Weak Battery: The original battery might be past its prime and unable to hold a charge effectively.
  • Faulty Regulator/Rectifier: This component regulates the voltage going to the battery. If it fails, it can lead to overcharging or undercharging.
  • Loose Connections: Corrosion or loose connections in the wiring harness can cause intermittent electrical problems.
  • Stator Issues: A failing stator can prevent the battery from charging.

How to Fix It?

  • Battery Replacement: Replace the battery with a high-quality AGM (Absorbent Glass Mat) battery.
  • Regulator/Rectifier Replacement: Test the regulator/rectifier with a multimeter. If it's faulty, replace it with a new or aftermarket unit.
  • Check Wiring Connections: Carefully inspect all wiring connections, especially around the battery, regulator/rectifier, and starter motor. Clean and tighten any loose connections. Use dielectric grease to protect connections from corrosion.
  • Stator Test: Have the stator tested to ensure it's producing the correct voltage.

3. Suspension Woes: A Bumpy Ride?

The MT-03 660's suspension is adequate for general riding, but it can feel a bit basic and underdamped, especially when pushed harder or on rough roads. Common complaints include:

  • Harsh Ride: The suspension feels stiff and uncomfortable, particularly over bumps.
  • Poor Handling: The bike can feel unstable and wallowy in corners.
  • Fork Dive: Excessive fork dive under braking.

What's Causing It?

  • Basic Suspension Components: The MT-03 660 comes with non-adjustable forks and a basic rear shock.
  • Worn Suspension Components: Over time, the suspension components can wear out, leading to reduced performance.
  • Incorrect Suspension Settings: Even though the forks are non-adjustable, the rear shock preload can be adjusted to suit the rider's weight and riding style.

How to Fix It?

  • Rear Shock Upgrade: Consider upgrading to an aftermarket rear shock with adjustable preload and damping. This can significantly improve the bike's handling and ride quality.
  • Fork Modifications: Several options are available for improving the forks, including:
    • Fork Springs: Replacing the stock fork springs with stiffer springs can reduce fork dive and improve handling.
    • Fork Oil: Changing the fork oil to a higher viscosity oil can improve damping.
    • Fork Emulators: Installing fork emulators allows you to adjust the damping characteristics of the forks.
  • Suspension Service: Have the suspension serviced regularly to ensure it's performing optimally.

4. Exhaust Issues: A Rattling Noise?

The exhaust system on the MT-03 660 is generally reliable, but some owners have reported issues with:

  • Exhaust Leaks: Leaks can occur at the joints between the exhaust header and the silencer.
  • Silencer Rattling: The silencer can develop a rattle, particularly at certain RPMs.
  • Corrosion: The exhaust system can be susceptible to corrosion, especially in areas with harsh weather conditions.

What's Causing It?

  • Loose Exhaust Clamps: Exhaust clamps can loosen over time, leading to leaks.
  • Damaged Exhaust Gaskets: Exhaust gaskets can deteriorate and leak.
  • Internal Silencer Damage: The internal components of the silencer can break down and cause rattling.
  • Exposure to Salt and Moisture: Exposure to salt and moisture can accelerate corrosion.

How to Fix It?

  • Tighten Exhaust Clamps: Check and tighten all exhaust clamps.
  • Replace Exhaust Gaskets: Replace any damaged exhaust gaskets.
  • Silencer Replacement: If the silencer is rattling internally, it may need to be replaced.
  • Corrosion Prevention: Regularly clean and protect the exhaust system with a corrosion inhibitor.

5. Other Minor Annoyances

Beyond the major issues, some MT-03 660 owners report smaller, but still noteworthy, problems:

  • Chain Adjustment: The chain requires frequent adjustment, especially with aggressive riding. Regular maintenance is key.
  • Instrument Panel Fade: The LCD display on the instrument panel can fade over time, making it difficult to read.
  • Paint Quality: The paint quality on some models is reported to be less than ideal, with chipping and fading occurring relatively easily.

Frequently Asked Questions (FAQ)

  • Why does my MT-03 660 stall when cold? A lean fuel mixture is a common cause. Adjusting the idle speed or remapping the ECU can often resolve this.
  • How can I improve the jerky throttle response? An ECU remap or the installation of a fuel management system like a Power Commander is the most effective solution.
  • Is the MT-03 660 a reliable bike? Yes, overall the MT-03 660 is a reliable motorcycle, but it's important to be aware of the common issues and address them promptly.
  • What's the best way to prevent electrical problems? Regularly inspect and clean all electrical connections, and ensure the battery is in good condition.
  • Can I adjust the front forks on my MT-03 660? The stock front forks are non-adjustable, but aftermarket options are available to improve performance.

Conclusion

The Yamaha MT-03 660 is a fun and engaging motorcycle, but being aware of its potential problems is crucial for a positive ownership experience. By understanding the common issues and their solutions, you can keep your MT-03 660 running smoothly and enjoy many miles of trouble-free riding. Don’t hesitate to consult with a qualified mechanic for any complex repairs or modifications.