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

  • Hi everyone,

    As you all know, Coffee (Dean) passed away a couple of years ago. I am Dean's ex-wife's husband and happen to have spent my career in tech. Over the years, I occasionally helped Dean with various tech issues.

    When he passed, I worked with his kids to gather the necessary credentials to keep this site running. Since then (and for however long they worked with Coffee), Woodschick and Dirtdame have been maintaining the site and covering the costs. Without their hard work and financial support, CafeHusky would have been lost.

    Over the past couple of weeks, I’ve been working to migrate the site to a free cloud compute instance so that Woodschick and Dirtdame no longer have to fund it. At the same time, I’ve updated the site to a current version of XenForo (the discussion software it runs on). The previous version was outdated and no longer supported.

    Unfortunately, the new software version doesn’t support importing the old site’s styles, so for now, you’ll see the XenForo default style. This may change over time.

    Coffee didn’t document the work he did on the site, so I’ve been digging through the old setup to understand how everything was running. There may still be things I’ve missed. One known issue is that email functionality is not yet working on the new site, but I hope to resolve this over time.

    Thanks for your patience and support!

125-200cc Power Valve Adjustments

MattR

MattR

2T Forum Clerk
Staff member
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?

powervalve_1_modified.jpg


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?

powervalve_2_modified.jpg
 
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
 
Thanks Kelly for the link. Here is Walt's discussion on Linkage Adjustment #1.

wallybean said:
....What is happening is that by adjusting the screw up it is pre-loading and creating a larger gap in the ramp cup that the balls work against to open the governor. This allows the balls to start farther from the center creating a larger centrifugal force and reducing the rpm needed to open the power valve. It doesn't effect anything else about the action so the pv's open the same way just sooner and not quite as far.

With the linkage adjusted all the way to the top, it is opening the pv almost 2000 rpm sooner, but total opening is only about 60%. While there is enough range of motion in the governor to allow it to open fully the ramp angles in the cups do not allow the balls to open the governor to its complete range. The earlier opening is doing exactly what the springs do and allow the flat spot to be eliminated. I would say that the power valves not opening fully probably don't affect hp until 9000+ rpm. So I worked with the adjustment to find where the happy medium was. With the bolt adjusted 1/3 of the way to the top you still had full range of pv movement and it lowered the initial opening by about 1000 rpm. At 1/2 the way up the pv's still opened about 80-90% and it lowered the opening rpm by about 1500 rpm. After more than 1/2 open there is a diminishing return as I could feel the loss on the very top. But the tighter the woods the less this is going to be an issue.

I love this stuff. The springs give you another option and the inner springs allow you to make the opening more progressive, but this is certainly an option that works.

Walt
Click to expand...

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???
 
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
 
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;70674 said:
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.
Click to expand...

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.
 
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
 
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