Why Does My Motorcycle Only Run With the Choke On?
My experience with the Yamaha 850 Triple at temperatures below 32 degrees Fahrenheit highlighted an issue with the choke. During rides, the engine ran smoothly without the choke at highway speeds, but at lower speeds, the idle was excessively rough, necessitating the choke. I suspect the carburetors were icing up, which is a common issue in cold climates.
However, during normal riding at warmer temperatures, the compromised fuel system became evident. In a lighter bike, like my 1977 Triumph Bonneville, I removed the choke (among other components) to reduce weight. The results were impressive; the bike weighed 350 lbs and outperformed anything comparable, with even Harleys being significantly slower. Interestingly, the inline 4 Honda did manage to outrun a stock Bonneville.
Common Causes and Symptoms
If your motorcycle runs only with the choke on, it generally means the engine is not receiving the proper fuel-air mixture. Here are some common reasons:
Clogged Carburetor
If your motorcycle has a carburetor, it could be restricted due to fouling or debris. This restricts fuel flow, making the choke essential to enrich the mixture.
Fuel Mixture Imbalance
The choke enriches the fuel-air mixture, allowing more fuel into the combustion chamber. If your bike functions only with the choke on, it indicates the mixture may be too lean, meaning there's not enough fuel.
Air Leaks
If there's an air leak in the intake system, it can dilute the air-fuel mixture, making it too lean. The choke compensates by adding more fuel to balance the mixture.
Fuel Filter or Line Issues
A clogged fuel filter or a kinked fuel line can restrict fuel flow, leading to similar symptoms. These components are crucial for maintaining a proper fuel supply.
Dirty or Faulty Spark Plug
A dirty or fouled spark plug can prevent the mixture from igniting properly, causing performance issues, and requiring the use of the choke.
Temperature
While the engine is cold, the choke helps it start and run until it warms up. If cold weather is the issue, the bike might require the choke just to start.
Steps to Diagnose and Fix
To troubleshoot and fix these issues yourself, follow these steps:
Inspect the Carburetor
Clean the carburetor and check for any blockages. Use a carburetor cleaner and a soft brush to remove debris and rebuild the unit if necessary.
Check for Air Leaks
Inspect the intake manifold and gaskets for any air leaks. Air leaks can be identified by listening for a hissing noise or by using a vacuum gauge.
Examine the Fuel System
Ensure the fuel filter and fuel lines are clear of obstructions or damage. Replace or clean fuel lines if they are kinked or clogged.
Check Spark Plugs
Replace or clean spark plugs if they are worn or dirty. Use a spark plug tester to check the condition and spark.
If you're not confident in your ability to address these issues, it's best to take your motorcycle to a professional mechanic for a thorough inspection and repair. Safeguarding the longevity and performance of your motorcycle is crucial, and a professional’s expertise can make all the difference.