125-200cc 125 power valves adjustment... I'm lost !

[Factory Squarna]

Hi I'm struggling to find a good regulation of the powervalves, on my 07 wr 125....

If I set the pv arm bolt almost all the way up (hence preloading le little spring) , the bike has a great spread of torque, but then it falls really flat on the top end ... I suppose that the valves don't fully open!

Then if I put the bolt down, the powerband will be very poor, pathetic, until the big midrange hit and finally good top end. Because this way the valves will start from a more opened position, and wont seal tightly at low revs, although its the only way to make them fully open!

I cant seem to find a middle spot that makes the valves open fully, and yet retain a decent sealing of the valves at low revs.... The bolt is actually between 1/2 and 3/4 up....

Also I cant see the point in making sure of the piston to valves clearance, a very stressed point on this engine as I read, if then when you adjust the pv arm bolt down you actually move the valves up from the rest position and enlarge the clearance!

Please give me your thougths because I'm sick to have a bike that can run fine only at low revs, or only on the top end, why cant it just run well all the way down to top like a ktm 125....
Such a shame because the handling of this bike is wonderful....

 

[johnnyboy]

See if Walt has any of his governer spring kits available if its that bad and have a play swapping them about, I dont have Walts springs but sourced my own and use them on the 165 and Trigs 125, Both bikes have great bottom mid and top with no noticable step coming onto the pipe.

 

[wallybean]

Did you remove the power valve linkage and check the upper connection where the tab fits over the slotted power valve shaft? If this connection is slightly loose or worn it will make it really hard to control the power valves correctly. Also I have seen several of the upper springs loose tension and eventually break. Pretty inexpensive parts to replace. Also have you pulled your power valve cover to make sure the little set screw that locks the lever arm to the power valve shaft is in tight? The older 7 port cylinders with the larger power valves tend to not need much tension to keep them closed. If you are having to go above 1/2 way up the adjustment slot to get tension then you have a problem somewhere.

 

[Factory Squarna]

Big thanks to Wally for the hints , something wasn't right as he mentioned ! I finally found out why my pv arm had a so small range of movement , the problem was in the upper arm, the one with the ball joint in it.

I saw in pictures of other husky's engines that this ball joint was in the internal side of the arm (near the spring), in my engine however this ball joint was in the external part of the arm, thus greatly limiting the throw of the arm itself !! this is what I have found :

so I cutted the ball joint and welded it in the other hole wich was already there (go figure why they made the piece with two holes if the ball joint was welded and not easily swappable... ) , this is the result:

mounted it all back together and now things start to make sense.... I can now set the lower bolt at exactly middle of the slot and the upper spring stays slightly preloaded, while before I had to set the bolt way up in the slot to achieve the preload...
Now with the bolt in the middle of the slot the valves are almost fully opening, way more then before with the bolt at the top, and yet they start from the closed position so the engine has good torque !

Still its not like a ktm engine, but now its decent, before it was pathetic !

I suggest everyone who has issues with the valves to check every part of the pv mechanisms , because each of these bikes seems to be built different from one another, since I discovered my issue with the ball joint !

Going offroading now, I'll be reporting back later