Reed Valve Symptoms

by Lynn Rademacher
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Reed valves are used in many two-cycle engines, including motorcycles, snowmobiles, and lawnmowers. Reed valves going bad can be difficult to diagnose as the symptoms can often be mistaken for problems. Most technicians will suspect a problem with the reed valves only after they have exhausted all other potential problems. Service technicians who work on two-cycle engines are familiar with the symptoms that bad reed valves can present with and are likely to diagnose the problem more quickly.


Reed valves help push air through a two-stroke engine that mixes with the fuel to create the combustion needed to create power. If the reed valves are cracked, they may not open all the way, which will reduce the amount of oxygen that gets into the engine to mix with the fuel. The result is a rough idling engine that sounds like it is on the verge of dying. Depending on the severity of the crack, the rough idle may disappear as the engine warms and the metal expands from the heat of running.


Engines with reed valves that are failing can present symptoms of hesitation during acceleration. The engine may fail to respond to the increased fuel flow and then jump forward as the gas is finally ignited. The hesitation in the engine due to failing reed valves can be very frustrating as the power is simply not available when needed. If too much fuel is poured into the engine and reed valves are failing, the result may be engine backfiring.

Reduced Power

Failing reed valves can result in reduced power at what should be cruising speeds. This can be a frustrating symptom as several other factors also can be present with reduced power as the symptom. However, failing reed valves reduces the fuel and air mixture. This results in fuel being dumped into the carburetor with no flame to ignite it. The result is reduced power. If the engine is brought up to the higher revolution per minute, or RPM, levels the power may return, but will disappear again once the RPMs drop.

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