1. 2 Stroke Husqvarna Motorcycles Made In Italy - About 1989 to 2014
     WR = 2st Enduro & CR = 2st Cross

125-200cc Power Valve Adjustments

Discussion in '2 Stroke' started by MattR, Jan 11, 2010.

  1. MattR 2T Forum Clerk

    Location:
    Temperance, MI
    Husqvarna Motorcycle:
    WB165, SM610
    Other Motorcycles:
    Yamaha FZ1
    I have been reading the various reports on the power valve spring adjustments. There was also some discussion on the linkage slots. I would like to learn more about the linkage itself and what effects the slots provide. I have modified 2 photos that I found (I think these were Walt's bike), but they show the 2 slots that I'm curious about.

    Linkage Adjustment #1:
    This vertical slot is located on the short arm connector to the govenor. This picture shows the bolt attached in the bottom of the slot.
    What effect on the PV occurs when the bolt is attached in the top of the slot?

    [IMG]

    Linkage Adjustment #2:
    This horizontal slot is located on the long arm connector to the power valve. This picture shows the bolt attached to the far rightside of the slot.
    What effect on the PV occurs when the bolt is attached in the far leftside of the slot?

    [IMG]
    MattR, Jan 11, 2010
    #1

  2. Motosportz CH Sponsor

    Location:
    Vancouver WA
    Husqvarna Motorcycle:
    2021 TE250i, 570 Berg, 500 KTM, 790R
    Other Motorcycles:
    many
    See the end of this post regarding the top pic.

    http://www.cafehusky.com/forums/showthread.php?t=7110

    The top pic will control when the PV opens and bottom how far. Jake said yesterday he thought sliding the bolt to the top of the slot (first pic) would open it earlier, the way I look at it it will open it later. As the bolt at the top of the slot means the PV ball and ramp have to move further out to start to move the PV. Dunno for sure but will be playing with it soon.

    here is a vid i did of mine when i was looking at what it was doing... http://www.youtube.com/watch?v=gDYRJkVU-hE
    Motosportz, Jan 11, 2010
    #2

  3. MattR 2T Forum Clerk

    Location:
    Temperance, MI
    Husqvarna Motorcycle:
    WB165, SM610
    Other Motorcycles:
    Yamaha FZ1
    Thanks Kelly for the link. Here is Walt's discussion on Linkage Adjustment #1.

    Anyone know what the Linkage Adjustment #2 does?

    Perhaps it can control how much the PV can travel. If the bolt was attached on the far left side, would the longer arm length allow the PV to fully open if used in conjunction with what Walt discusses above???
    MattR, Jan 11, 2010
    #3

  4. wallybean Mini-Sponsor

    Location:
    Montana
    Matt,

    By moving the ball joint out to the farthest hole you will limit motion of the pv and enhance progressiveness although that is pretty limited with a single rate spring. If you do them both at the same time you you will not get the pv open very far. :) BUT I think I am going to try the ball moved out with my stiffest inner spring tomorrow and see how much progressiveness I can get out of it.

    The search for the perfect powerband goes on.:applause:

    Walt
    wallybean, Jan 11, 2010
    #4

  5. Motosportz CH Sponsor

    Location:
    Vancouver WA
    Husqvarna Motorcycle:
    2021 TE250i, 570 Berg, 500 KTM, 790R
    Other Motorcycles:
    many
    Walt, does moving the bolt up in the slot (first pic) delay the PV opening or advance it?
    Motosportz, Jan 11, 2010
    #5

  6. wallybean Mini-Sponsor

    Location:
    Montana
    Kelly,

    It advances it/ opens faster. I did a little write up on what I found this afternoon in the no more bog thread. I would try yours with it moved half way, Still get the pv open most of the way and it drops the opening rpm.

    I will do more tomorrow with some different springs thrown in for comparisons.

    Walt

    As I have said before once the balls move out the force goes up exponentially with rpm. That is why you get that opening at a lower rpm.
    wallybean, Jan 11, 2010
    #6

  7. Motosportz CH Sponsor

    Location:
    Vancouver WA
    Husqvarna Motorcycle:
    2021 TE250i, 570 Berg, 500 KTM, 790R
    Other Motorcycles:
    many
    Thanks Walt. Was this something you observed? The reason i ask is because looking at it it seems like it would open later with the bolt at the top of the slot because it seems the ball and ramp would have to move further (higher RPM) before the arm started to move as it seems like it would be preloaded more. Pure speculation on my part as I only had it apart to install the PV's.

    when you move the bolt to the top of the slot does the PV now become partially open when the motor is off? That seems wrong as well.

    - it did make a good difference on Shanes bike just trying to understand why.
    Motosportz, Jan 11, 2010
    #7

  8. wallybean Mini-Sponsor

    Location:
    Montana
    Kelly,

    What it does is pre-load the governor spring/keeping it partially deflected. At the same time it keeps the pv's shut and would actually pull it past shut if the spring up above didn't counteract this force. The reason that the pv is opening sooner is strictly a matter of having the governor slightly open and the balls allowed to start farther out from the central shaft of the governor. This creates a much greater force sooner than if the governor was completely closed forcing the balls into the center. Tie a nut to a string and vary the amount of string you let out of your hand as you spin it in a circle. This will really illustrate the greater force you have to exert to maintain control of the string the farther out the nut gets and still maintain the same rpm. Now multiply this by thousands of rpms and you get the feel for whats going on. Remember the governor spins at 1.2 times the actual engine rpm.

    The WR 250/300 spins its governor at 1.7 times the speed of actual engine rpm. This is how they get a much stiffer spring to open the pv's at approximately 6000 rpm. The spring kit for the larger WR's contains much larger differences in spring rate from one to the next because the centrifugal forces involved are much greater. So to get a relatively significant change in opening rpms it takes much greater change in resistive forces(springs). Completely TMI :)

    Walt
    wallybean, Jan 11, 2010
    #8