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2008 Powervalve questions

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I have seen some threads talking about adjusting the powervalve screw but I have not seen info on the following...

1.) What does the manual for a 2008 300XC-W say not to adjust it? Is there any harm that you can cause?

2.) What is the standard adjustment to start with after putting in a new spring?

3.) It seems like the adjustments of the screw can overlap the range of the next higher or lower spring meaning you can get green spring performance from a yellow spring if you back it out all the way.

Your thoughts?

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It's strange, they give you a screw to adjust, then tell you not to adjust it. :banana:

I read a whole thread on KTM talk about 'balls falling out of holders' or something, then realized they were talking about 200's, which have a different power valve set-up.

Don't think there is overlap with adjustment/screw and spring combinations.

Asking which spring to run is like asking which oil is best. :busted:

Wondering myself if I've ruined my new bike by turning that screw. :smirk:

Good news is, I can take off a cover and see if it's working properly. Don't ask me which cover, I read the thread on KTM talk late at night and sent myself a link for reference later on, when I get time. Since I'm posting all this drivel, I think that means I have time and should get off the interweb.

What's up Tom? Let's ride trail 6 again one of these days on our 300's. :bonk:

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I have seen some threads talking about adjusting the powervalve screw but I have not seen info on the following...

1.) What does the manual for a 2008 300XC-W say not to adjust it? Is there any harm that you can cause?

2.) What is the standard adjustment to start with after putting in a new spring?

3.) It seems like the adjustments of the screw can overlap the range of the next higher or lower spring meaning you can get green spring performance from a yellow spring if you back it out all the way.

Your thoughts?

1. No harm, adjust all you want as long as you don't go too far. don't question why, just know that it is ok.

2. Are you talking range? about 3 turns I believe. It's been awhile though.

3. There may be some slight overlap, but I doubt it. The springs have different rates, so even with more preload on a lighter spring, it still won't likely behave just like a heavier spring. And, you are thinking in the wrong direction, to get closer to the green, you would put more preload on the yellow spring, screwing the adjuster in.

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I believe that you can go as much as 4 1/2 turns in or run it flush. Flush or closer to flush, gives the quickest hit.

Green spring is the most mellow

Yellow spring is next as far as punch goes.

Red is the quickest, especially when you run the toggle flush.

I have heard that there is also a blue spring, that runs between yellow and red.

Jetting, head work and carb bore also make a huge difference.

I just had my head done by Trey at Wildcat Motorworks and it makes a huge difference the way the bottom end runs. Next I am going to have the carb bored for more mid and top end.

Edited by mvertoch
ch

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Adjust all you want. The concern is if you go too far in you will come out of the adjuster housing. The adjuster threads in from the inside of the housing (the housing is the part held on by 2 bolts). Lean the bike over to the left side, so oil won't run out. Then you can remove the 2 pv housing bolts and see how far you can turn it in before in comes out of the threads.

check out this trick piece I picked up. It allows on the fly pv adjustments, without any tools. i use it frequently on moto days or when the trail conditions are extreme.

DSCF3271.jpg

DSCF3273.jpg

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I have seen some threads talking about adjusting the powervalve screw but I have not seen info on the following...

1.) What does the manual for a 2008 300XC-W say not to adjust it? Is there any harm that you can cause?

2.) What is the standard adjustment to start with after putting in a new spring?

3.) It seems like the adjustments of the screw can overlap the range of the next higher or lower spring meaning you can get green spring performance from a yellow spring if you back it out all the way.

Your thoughts?

Good questions

1. There is no harm in adjusting the spring preload. The adjuster has a travel stop, so experiment as much as you like, you can't harm anything.

2. About 3.75 turns in from flush with the engine cases.

3. Spring rate and spring preload are not the same thing. Spring preload (which is adjustable via the screw) determines the RPM at which the powervalve flap begins to open. Spring rate (which is determined by green, yellow, or red spring) determines how quickly the powervalve moves from closed to fully open.

If you want more, check out this Powervalve FAQ.

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3. Spring rate and spring preload are not the same thing. Spring preload (which is adjustable via the screw) determines the RPM at which the powervalve flap begins to open. Spring rate (which is determined by green, yellow, or red spring) determines how quickly the powervalve moves from closed to fully open.

Adammoto nailed it in the head with this quote!

I will add that I have played with the yellow and red springs and ALL of the PV adjustment. I do not think there is any overlap between the springs using the adjustment. But the good thing is you can tailor the power delivery to your liking, it is greatly adjustable.

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Thanks for telling us the difference between spring rate/preload settings, I didn't know that. So with the green spring flush, it will open late and fast? Which will means there's no 'blubbering' or hesitation when it finally opens? So it's more of a seamless transition from closed to open? Seems that's my experience. My goal is to have it be smooth at low revs, and then open fast when I fan the clutch, to shoot out of corners. Green spring flush was almost getting it done, but I might have to go back and try yellow with it turned in a couple notches, since it wasn't coming on power with a fast fan of the clutch.

Maybe you can tell us what the ignition switch actually does? I think it retards the timing? So it reduces the horse power at low revs... or maybe it reduces power all across the power band?

You should be able to remove the left side PV cover (non pipe side) the start the bike up and rev it. With the cover off you should be able to see if it is moving or stuck.

http://ktmtalk.com/index.php?showtopic=439032&hl=300+power+valve+adjust

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Thanks for telling us the difference between spring rate/preload settings, I didn't know that. So with the green spring flush, it will open late and fast? Which will means there's no 'blubbering' or hesitation when it finally opens? So it's more of a seamless transition from closed to open? Seems that's my experience. My goal is to have it be smooth at low revs, and then open fast when I fan the clutch, to shoot out of corners. Green spring flush was almost getting it done, but I might have to go back and try yellow with it turned in a couple notches, since it wasn't coming on power with a fast fan of the clutch.

Maybe you can tell us what the ignition switch actually does? I think it retards the timing? So it reduces the horse power at low revs... or maybe it reduces power all across the power band?

http://ktmtalk.com/index.php?showtopic=439032&hl=300+power+valve+adjust

1st gear -

You have the right idea...but check this out. The spring force holds the powervalve flap closed. The exhaust gasses try to push the flap open as RPMs increase. So the green spring (heaviest spring rate) set to flush with the cases (very little preload) will allow the flap to begin opening earlier in the RPM range - where preload has the greatest influence - but open more gradually rather than with a lighter spring.

By your description, it sounds like you might want to try the yellow spring at 3 turns in from flush with the cases. If the bike is blubbery on the low end, consider jetting as well.

And yes, the ignition switch retards the timing a little. Its pretty subtle compared to the PV adjustment though, don't you think?

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Thanks for the explanations...

I was playing around and since I am new to the bike I tried the green spring but if I turned the screw in more than 2 turns the transition to real power came too slowly. I left it at around 1 turn. I generally ride fairly tight technical stuff so it needs to be smooth but I need to be ready to leap!

Now I just bought a map switch so I can see what that does now that the spring is set.

I will then try the yellow spring.

BTY I use a flat blade screwdriver to turn the spring and I store it behind the number plate stuck into some tubing. I use a bit of loose zip tie secured to the plate and like a collar for the screwdriver to keep the top of it from moving around too much.

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Thanks for the explanations...

I was playing around and since I am new to the bike I tried the green spring but if I turned the screw in more than 2 turns the transition to real power came too slowly. I left it at around 1 turn. I generally ride fairly tight technical stuff so it needs to be smooth but I need to be ready to leap!

Now I just bought a map switch so I can see what that does now that the spring is set.

I will then try the yellow spring.

BTY I use a flat blade screwdriver to turn the spring and I store it behind the number plate stuck into some tubing. I use a bit of loose zip tie secured to the plate and like a collar for the screwdriver to keep the top of it from moving around too much.

You wont see a big difference with the map switch until you have a head mod done. I thought they were a waste of money until I had my head done.

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Red spring with no preload. Use the throttle to control the hit. This way when you do want a hard hit at low rpm it's there. You can;t back the adjuster out to far. It has a hard stop.

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More great advice, thanks. Yep, been thinking about going back to stock yellow spring, a couple turns in. Spring selection depends on conditions, how good traction is. Did a real snotty enduro, the yellow was giving too much wheel spin so I swapped out to the green... but the next ride was in dry conditions and the bike needed more hit. As I get used to the bike, I can use more power at low revs, but still not ready for red spring. Throttle control is the key since the bike can spin up, lose traction, then the 4 strokes walk away. A throttle cam might help, so I've heard. Guys who say to just use the red spring are typically riding pre 10 bikes. The '12 has the V4 reeds and friends with the older bikes comment on how tight my '12 sounds, so I think we can't compare the older bikes directly with the new. With a fan of the clutch and a blip of the throttle, the bike will spin up/wheelie in any gear, any spring, so red spring is over kill for anything less than perfect traction.

The ignition switch is probably not necessary, except for those really snotty/snowy/icey situations... and for mellowing the bike for new riders. Pretty much leave it on the 'wild' setting now after getting used to the bike.

1st gear -

You have the right idea...but check this out. The spring force holds the powervalve flap closed. The exhaust gasses try to push the flap open as RPMs increase. So the green spring (heaviest spring rate) set to flush with the cases (very little preload) will allow the flap to begin opening earlier in the RPM range - where preload has the greatest influence - but open more gradually rather than with a lighter spring.

By your description, it sounds like you might want to try the yellow spring at 3 turns in from flush with the cases. If the bike is blubbery on the low end, consider jetting as well.

And yes, the ignition switch retards the timing a little. Its pretty subtle compared to the PV adjustment though, don't you think?

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Good questions

3. Spring rate and spring preload are not the same thing. Spring preload (which is adjustable via the screw) determines the RPM at which the powervalve flap begins to open. Spring rate (which is determined by green, yellow, or red spring) determines how quickly the powervalve moves from closed to fully open.

I don't think that's true. Both spring preload and spring rate determine the rpm the powervalve opens and has nothing to do with how fast the powervalve fully opens. In the KTM manual the breakdown says the color spring and the rpm which the powervalve will open using that spring.

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Kalashnikov -

1. Spring rate is force over distance, like "2 kilograms per millimeter" (2 kg/mm). This means that for every 2 killograms of force you add to the spring, it will compress another millimeter. So to compress the spring 1 mm, you need a 2 kg weight on top. To compress the spring 2 mm, you need a 4 kg weight. ...and so on.

2. Preload does not change the spring rate. By compressing the spring a set distance, it determines the initial force required for additional movement. For the spring in the example above, lets say we preloaded the spring 4 mm. That means 8 kg of force is pressing against the preload collar. But...to compress the spring an additional 1 mm, it still just needs an extra 2 kilograms, same as before.

3. However, if we swap out the spring to a heavier one with a rate of 4 kg/mm, the force required to move the spring +1 mm is always +4 kg. To move it from 0 to 1 mm > 0kg + 4 kg = 4 kg. To move it from 10mm to 11mm > 40kg + 4kg = 44 kg. It is always +4 kg.

4. The powervalve spring is connected to the powervalve flap via a link arm. The spring must compress a certain distance to allow the flap to open all the way. The heavier green spring requires more force to reach that distance than does the lighter red spring. Hence, the heavier the spring rate, the more force is required to fully open the powervalve.

Hope that makes sense.

Edited by Adammoto

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