Yamaha powervalve adjustment

[alexbrown64]

OK, just a question on the Yamaha power valve.  This one is on an 83 YZ125.  In the first pic, i can align the groove in the linkage with the hole in the case but i cannot put the second linkage plate on if i do this as it there is not enough adjustment in the plates so that it will stay in that position. The Yamaha manual shows a pic of the groove/hole aligned without a pin in.  The pin is only used to undo/tighten the nuts.  Alignment of the groove/hole should happen with the linkage relaxed and no pin necessary.  I dont have the adjustment in the plates for that to happen unless i do not fit the large linkage plate.



If i lift the large plate onto the powervalve, it throws out the groove/hole.  There is no adjustment left to align the groove/hole properly.  If i do align them, i have to lift the linkage rod up and tighten the nuts.  When i let the linkage relax again, it goes back down and turns the powervalve clockwise and misaligns the groove/slot.



This the the postition it ends up in with maximum adjustment of the plates and the linkage relaxed.



My questions are: Can you run the large linkage plate out of the powervalve boss as this is the perfect alignment but does not look right. (See pic 1)

I compared my linkage to a new one i have and it looks and measures exactly the same.  I rebuilt the governor to exact spec and photos of original, so where is the misalignment coming from.
What is the fix for this?  I could adjust the groove in the governor so the linkage sits relaxed in another position, i could put the new linkage on etc.. but does anyone have the correct way to fit adjust these valve.

Cheers,
Alex

[rocketfrog]

So the shim stack in the governor is assembled in the correct order for sure? The governer fork tends to wear the pins flat where they engage in the groove, this can be the cause of some lost motion in the system but that would not really explain the inability to rig the system correctly. Let me have a look at the pics when I get home tonight and see more precisely where you are at. It will be something simple for sure.

Initially, I would say that the governor is assembled incorrectly and the relationship of the groove does not match the null position of the valve.

[alexbrown64]

Thanks rocketfrog, i know exactly what you mean. All the forks wear where the fork goes into the governor but you wouldn't think it would throw it out so much. I picked up my governor and realized the spring was floppy.  My spare governor (from an L) had a helical gear but had a tight spring.  Using pics and diagrams, i rebuilt one good governor and the spring felt perfect.  The previous owner must of had it apart and left a few spacers out..  The governor shims were all over the show, so i put them back to stock based on the manual and pics from the internet.  I have included a pic here of what it now looks like.  Perhaps the previous owner stacked the shims differently to work around the problem. 




I have a new power valve linkage, but i only use it to compare wear against my old ones.  The used one in this case was OK, so i re-fitted it.



Another interesting fact is that i have my two YZ125K's apart at the moment and both have exactly the same problem and the same amount of adjustment out. So maybe the wear in the linkage fork is an issue and throws the whole thing out a bit.


Cheers,
Alex

[alexbrown64]

I think i may of answered my own questions.  I have a spare clutch cover, linkage and governor. I measured everything up, and then removed one 1mm shim from the left side of the governor (see pic above) and put it on the right side of the spacer.  This effectively moved the spacer that the linkage fork sits in over 1mm.  It made a 5-6mm difference to the height of the linkage going up to the power valve.  This "lengthens" the linkage and brings the groove in the linkage anti-clockwise back to the hole in the case.  Has anyone had to do something similar?  I will try it on both bikes when i get a chance.  I am still putting the top ends on them and plumbing everything back up..... see yz125k thread.

Cheers,
Alex

[Ekka]

Alex when u hook up the power value dose it open the value up from the standard position

[alexbrown64]

Hi Ekka, The first plate sets the valve.  You slip it on the boss (with the dot facing up) and align the slot and hole with a pin.  When i do this, i can look up in the exhaust port and see the power valve "closed" and covering roughly half the port.  When i put the linkage on (i have to lift the linkage to get it on the boss) and then let it settle (the linkage is pulled back down by the governor) the power valve is rotated clockwise. This has the affect of closing it more, except that it is all ready fully closed "half the port covered" but just rotates it more that way.  When the bike revs, the linkage goes up, turning the power valve anti clockwise which opens the port.  Because i could not get the adjustment the way it was, i believe i would of been over closed and the linkage would not be able to fully turn the power valve and open the port to maximum.

I did play with the governor this morning.  I took a shim from one side and put it on the other side of the groove that the linkage sits in.  It worked perfectly.  With just a 1mm shim, the linkage was reset to the proper position allowing proper adjustment.

I was up at 4am and worked through to get the old girl going.  It took off like a scolded cat.  Felt like a hooligan racing up the street with no helmet on "running it through the gears".

Just need to sort a few small problems with the carb and she will be all good to go.



Cheers,
Alex

[rocketfrog]

Alex, it is good to hear the scourge of the suburban neighbourhood is alive and well. You can only guess what folks were thinking when their sleep was rudely interupted by a 2 stroke hoon. I believe you have solved the issue with the PV on your 125 there mate. If everything lines up as it should , and it operates well by the sounds of things, I would say you have it sorted.

The YZ125K is a good thing, a very exciting hit when the motor comes on song from my recollection. The last time I rode a 125K I was stepping off a 125J at about age 16. Such a different bike in every regard.

[Ekka]

No worries Alex I was thinking if the value wide open it was doing same thing to what my 250 was doing