In its most basic form, a 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 very limited on what their power bands could do. One power band might be able to produce a rush of power in the low-to-mid rev ranges. Another power band may have created a power rush in the mid-to-upper-high rev ranges. Still, another might produce a lot of power 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 exhaust produced from the engine controls the mechanical valves. Electrical valves come equipped with electrical controls that allow more control over the valve and more precise tuning.
How Do Power Valves Work?
As I stated earlier, the power valve’s main function is to regulate the size of the exhaust port. This regulation in size will directly influence the size of the power band. If the size of the exhaust port is smaller, then the powerband becomes wider. If the size of the exhaust port is wider, then the band becomes smaller.
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 in the valve and effectively closes the valve as needed.
One of the significant advantages of having a power valve installed in a two-stroke engine is that it allows the engine to produce much more power throughout a broader range of RPMs. Even more, power valves can be manually adjusted to fine-tune the amount of power you receive at different rev levels.
As I touched on 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.
A Brief Word on Power Valve Durability
As advancements develop in power valve construction, power valves as a whole seem to be getting more and more durable. With that being said, 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 valve. These things build up carbon regularly and thus need to be regularly cleaned. A good rule of thumb is to clean and readjust the power valve (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 bad 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!
If you have any questions or anything to add, please leave them in the comments or on our FaceBook page!