Many people don't even know how important a role the power valve plays. The power valve is mostly used in two-stroke engines to regulate the flow of exhaust gases.
Since two-stroke engines do not have intake and exhaust valves, the expansion chamber and the muffler determine the outflow of exhaust gases. Which in most cases is too opened, i.e. the exhaust gas flows out too easily (at the same time, it also sucks out unused gasoline-air mixture). That is, at lower speeds (at partial load) it would result in the engine being weaker and less efficient. The power valve is designed to prevent the easy outflow of gases, thereby retaining the fresh fuel-air mixture in the cylinder.
In many models, the operation of the power valve can be controlled by turning a simple screw in and out. For example, in the case of the KTM EXC250TPI I use, when I turn the adjusting screw inward, the valve opens "slower", so the throttle respond will snappy and unpredictable.
By adjusting the power valve, the same bike can show a completely different character. By rolling out, the motorbike can be handled much more accurate, especially when driving on wheelie, this is very important. But unfortunately, this is accompanied by the fact that it is less prone to wheelie (it needs more throttle and higher rpm). Conversely, if you turn the screw inward, on my vehicle it is possible to get it to pop a wheelie relatively easily even in 4th gear. But with such a setting, controlled wheelie becomes difficult, because the throttle response will be too sudden.
In summary: feel free to try adjusting the power valve, because roughly 2-3 complete turns will result in a completely different character.
My suggestion is to unroll it completely and turn it in every half turn, until the bike comes to wheelie relatively easily, but you can still apply the throttle gently while on wheelie.
Bonus tip: you don't need any special tools as you can see in the picture.
Bonus tip 2: if you found the approx. correct setting, then mark the screw and the casting visible next to it with an alcohol, permanent marker.
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