Posted By: Nick Keller
This “How to” article applies to the KTM 125 / 144 / 150 / 200 bikes ONLY. The 250 / 300 / 380 bikes use a different style of PV adjuster where you change springs, and have a different style of adjuster mechanism. Make sure to wash and clean your bike! You don’t want to get dirt in some of this stuff (but that is sort of a rule anytime you work on your bike, right?).
1. First, pull the cover plate on the left side of the engine, where the black hose and gray elbow are.
2. What you will probably see is something like this. It will be a bar with a horizontal mark, inside a window with a horizontal mark at the top. Your marks will probably be close to the top of the window like this.
3. What you are looking at is the power valve arm that opens and closes the flapper and sub-ports in the exhaust port. This gives you a variable-height exhaust port. One hell of a piece of engineering by the way! Here’s a shot of what it looks like inside. Note the arrow I drew, that is the mark you see through the window. Here is the PV fully closed [TOP] (note the mark is high in the window) And fully opened [BOTTEM] (note the mark is low in the window):
OK, now adjustment how to adjust
let’s make sure everything works. When the bike is running, the arm should move in conjunction with the throttle. When you rev the bike up the mark should go down, when you let off the throttle, the mark should go up. Kind of opposite of the throttle settings huh? If it doesn’t, there is something wrong with the governor mechanism (that’s another write up if you have problems).
4. On the right side of the bike is a large nut with a copper washer under it. THIS IS NOT YOUR ADJUSTER!
5. The adjuster lives under it, you have to remove this nut and washer, (don’t lose the washer), to get to it.
6. The adjuster should be moved with a wrench like this:
7. First, you have to loosen the small hex bolt down about 4:00 o-clock. Don’t take it out; just loosen it about 1 turn. Under that bolt is a rubber plug that holds the adjuster so you can work on it and ride at the same time. I’ve found this rubber plug gets hard (or falls out if someone else took the bolt out) and doesn’t hold. You can cut a piece of o-ring to work if needed. To make sure I get the setting I want, I adjust the mark first, tighten the 4:00 o-clock bolt, replace the big nut and copper washer, and then go test ride. Longer? Yes. Sure to work every time? Yes. Turn it counter clockwise to move the hit further up the throttle curve (later in the power band) and clockwise to move the hit further down the throttle curve (earlier in the power band). Here’s an idea of what you get. The Langston setting is from a KTM mechanics article in one of the MX magazines and refers to where some of the factory Pros like to run their PV:
8. Here is where I like to run mine, it’s a little lower than the Langston; this is a great setting for a trail rider or novice Motocross racer:
9. Most bikes have the mark somewhere near the top of the window. The higher the mark, the later the two stroke hit occurs. Some people like the later hit, some don’t. I like the Power Valve to open sooner, and have the hit come in at about ½ to 5/8 throttle. The late hit feels flat or lean to me, but that might be just the feel you like. Generally, higher is milder, lower has more punch.