A 2-stroke power valve is nothing more than a piece of metal slid into the engine’s exhaust port. Its primary function is to regulate the size of the exhaust port, thus enabling the engine to deliver controlled power throughout the rev range.
Back in the day, two-stroke engines were restricted on what their power bands could do. One power band might be able to produce a rush of power in the low-to-mid RPMs. Another powerband may have created a power rush in the mid-to-upper-high RPMs. Still, another might kick in only at the top-most range. There were no in-between, and there were no power surges present in all ranges.
But then the power valve was introduced to the two-stroke engine, and everything changed.
Today, power valves exist in both mechanical and electrical formats. The engine’s speed controls the mechanical valves. Electrical valves come equipped with electrical controls that allow more control over the opening and more precise tuning.
How Does It Regulate The Power?
The power valve’s primary function is to regulate the size of the exhaust port. This regulation in volume will directly influence the position of the power band in the RPM range. If the size of the exhaust port is smaller, the exiting airflow is restricted. This restriction will reduce the power potential of the engine. When the exhaust port is open, more air can flow, and the engine can make more power.
The opening of the exhaust is where the term “on the pipe” comes from. What RPM the power hits depends on your exhaust valve and expansion chamber configuration.
Regardless of the type of the two-stroke dirt bike engine, the power valve will close at low RPMs and open at high RPMs. The way it achieves this is via the valve’s governor. The governor overpowers the spring pressure keeping the flap closed and regulates the flap from closed to completely open, depending on engine speed and RPM.
One of the significant advantages of having a power valve in a two-stroke engine is that it allows the engine to produce much more power throughout a broader range of RPMs. Even more, these valves can be manually adjusted to fine-tune the amount of response you receive at different RPM and throttle position.
As I mentioned earlier, the valve has its spring. That spring can be adjusted, either manually or electronically, to change its tension. That tension change will have different effects on how the power distributes across the rev range.
Keep Your Dirt Bike Maintained!
As advancements develop in power valve construction, they as a whole seem to be getting more and more durable. The two-stroke power valve is still susceptible to damage. Therefore, it’s essential you know what some of the major causes are for power valve malfunction and damage.
One of the leading causes of power valves failing is the lack of proper maintenance on the components. These parts build up carbon regularly, and you need to clean them periodically. A good rule of thumb is to clean and readjust the mechanism (if required) every seven to fifteen running hours.
Two other common causes of power valve failures are backfiring and improper torque levels (too tight or too loose).
It’s also important to note that some valves can malfunction right out of the factory, so make sure you check it before installation and perform a test run after installation.
The most noticeable symptom of a malfunctioning power valve is a complete lack of power at high RPMs. Keep that in mind the next time you can’t make it up that hill!
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