1. Idle adjustment is too low: Check your owner's manual to confirm that the idle speed adjustment screw is set correctly. If the idle speed is set too low, the engine will stall when you come off throttle.
2. Idle circuit is dirty or clogged: The idle circuit allows fuel and air to bypass the main carburetor when the throttle is closed. If the idle circuit is dirty or clogged, it can restrict the fuel and air flow and prevent the engine from idling properly. You can clean the circuit using carburetor cleaner and compressed air.
3. Choke is stuck partially open: The choke enriches the fuel mixture when the engine is cold. If the choke is stuck partially open, it will continue to enrich the mixture and prevent the engine from idling properly. Ensure the choke is fully closed when the engine is warm.
4. Vacuum leak: A vacuum leak can cause the air/fuel mixture to become lean, causing the engine to run erratically and stall when you close the throttle. Check the hoses and connections around the carburetor and manifold to ensure they are sealing properly.
5. Electrical issue: A faulty ignition component or electrical wiring can also prevent the engine from returning to idle. Check all the connections around the ignition system and ensure they are secure. You may also want to check the spark plug to ensure it is in good condition and generating a strong spark.
If the problem persists after checking all these things, you may need to take the ATV to a qualified repair technician.
