Idle is useful for warming up your motorcycle engine. But after it’s reached the necessary temperature, leaving it at idle will make it stall. A common example is when waiting at a red light.
In this article I want to share the five most common reasons why a bike dies at idle, and the best ways to fix these issues without spending hundreds of dollars to hire a pro.
Bike Dies at Idle: 5 Common Causes and Solutions
The Modern Fuel Injected Engine
The most common reason for your bike dying on idle is that the modern fuel injected engine runs on a very lean air/fuel ratio. This is the most likely cause but there are others to consider, especially if the problem is recent and hasn’t bothered you in the past.
Engine idle level set too low
Unfortunately, on newer motorcycles the idle level often can’t be changed. If it can be changed, it’s done by either using the adjustment knob if there is one, or adjusting the idle screws on the carburetor. In any case, this is a relatively easy two step process:
Place your motorcycle in neutral and start the motor. Let the motor run for a few minutes to warm up. Once warm, take note of the motorcycle’s engine idle speed. Most motorcycles require an idle speed of 1,100 to 1,300 RPM (revolutions per minute) to operate properly at a standstill.
Turn the idle screw slowly using a screwdriver, twisting the screw counter-clockwise to lower the motor’s RPM or clockwise to increase RPM. Stop adjusting the screw when the tachometer indicates the desired RPM range.
Twist the throttle open a few times and observe the tachometer needle as the RPMs fade. The needle should return to the desired idle speed. If not, readjust the idle and test it again.
Clogged charcoal canister in the fuel tank ventilation line
If the charcoal canister is clogged, it will prevent the gas fumes from entering or exiting the canister and cause all sorts of trouble. So it’s important to clean the canister when it happens. Here’s how to do it properly:
Remove the charcoal canister by removing the top and bottom lines from the canister with a flat-head screwdriver. The canister has three lines on top and one line on the bottom. Use a ratchet and a socket if needed to remove the canister from the bracket.
Place the charcoal canister on a flat surface. Start the air compressor up and let the air pressure build up to at least 50 psi. Shut the compressor off once the air pressure reaches the 50 mark.
Insert the rubber tip of the air line nozzle fitting into the outer vent control valve pipe that is on top of the canister. This pipe is separate from the other two top pipes. The outer control pipe is the on the very end of the canister. The outer control pipe is also a little bit bigger than the other two pipes.
Place the ends of your fingers over the openings of the other two pipes on top of the canister with one hand. Pull the air release trigger on the air line nozzle and allow the 50 psi of air to blow into the canister with the other hand. Continue blowing the air into the charcoal canister for about one to two minutes. Remove your fingers from the top pipes and place one of your fingers near the front opening of the pipe on the bottom of the canister.
Apply the air to the opening of the control valve pipe again and use your finger to determine if the air is coming out of the bottom of the pipe. This will ensure that the canister is clean and allowing air flow from the top of the canister to the bottom pipe of the canister. Reinstall the charcoal canister.
Faulty Lambda (Oxygen) Sensor
A Lambda sensor measures the amount of unburned oxygen in a motorcycle’s fuel exhaust.
If the oxygen level is too high or too low, the Lambda sensor sends a signal back to the bike’s computer that tells it to adjust the air/fuel mixture so that the bike can perform optimally and within emission control standards.
If the sensor is damaged, the bike engine can stall at idle and suffer from other related issues, such as poor mileage, catalytic converter failure, decreasing engine power at cruising speed etc.
You can test your motorcycle’s oxygen sensor and see if it’s working properly or should be replaced. Here’s a video explaining how to test it:
Fuel pressure too low
This problem is usually caused by a faulty fuel pump and may cause your engine to stall/die at idle. Common symptoms of a faulty fuel pump include:
- A Whining Noise is Coming from the Fuel Tank
- The Engine Stalls/Won’t Start
- The Bike Surges
If you’re experiencing these problems, consider checking your fuel pump to see if it’s working correctly. Here’s a great video tutorial for doing exactly that:
Valve clearences too tight
There are many problems associated with tight valves. Mainly, the bike won’t idle cold, it will hang up at high idle when coming down from speed, and the fuel econ will be 25-40% lower.
Tight valves also lead to worn valve seats and deformed valves. This can lead to carbon deposit on the seat and reducing the fill and exhaust of gasses.
There is no reason to run a tight valve at all. The perfect balance is a smooth running engine with minimal valvetrain noise. Setting the valve loose has it’s own problems, so it’s best to take a centrist route on this one and have it neither too tight nor too loose.