Possible Causes:
1. Idle speed adjustment: The idle speed knob may need to be adjusted. To adjust idle speed:
- Turn the idle speed knob clockwise to increase the idle speed and counter-clockwise to decrease the idle speed.
- The ideal idle speed is approximately 1300-1500 RPM.
2. Incorrect fuel mixture: The fuel mixture might be incorrect, causing the motorcycle to be too lean or too rich. If the motorcycle runs better with the choke on, it may indicate that the fuel mixture is too rich, and needs to be adjusted.
- If you have any modifications or aftermarket parts installed on the motorcycle (such as an exhaust system, carburetor, or air filter), these can affect the fuel mixture and require adjustment.
- Check the air filter and make sure it is clean. A dirty or clogged air filter can cause the motorcycle to run too lean.
- Check the fuel system, fuel line, and carburetor for any clogs, debris, or leaks that may be restricting fuel flow.
- If the problem persists, you can also try adjusting the fuel screw, which is usually located on the bottom or side of the carburetor.
3. Spark plug issues: A worn-out or damaged spark plug can also cause poor idle. Replace the spark plug if it is old or damaged.
4. Faulty carburetor: If the previous checks do not resolve the issue, there could be an issue with the carburetor itself. Carburetors are a complex system with several components, and faults can manifest in various ways, including erratic idling and a reliance on the choke for operation.
Note: These are just a few common causes of idling problems on a TTR90. It's important to thoroughly inspect the motorcycle to identify the specific cause of the issue.
