Posts
922
Joined
8/9/2010
Location
Thompsons Station, TN
US
Edited Date/Time
6/5/2020 7:30pm
So I received the F1 moto arms and they seem to fine but powervalve is still sticking. It seems the barrel that spins in the cylinder is too tight. If I back off the cover bolts it works perfect but once you tighten the bolts it binds the pv and will not let it move. I have cleaned and lubricated everything but still no luck. I have heard of people having to buy another cylinder to solve the problem. I'm thinking you could machine the cover or cylinder a few .001 and cure it. I'm probably going to send the cylinder to Terry Varner.
It makes you wonder how many KTM's are not running to potential because of this.
Bad design...
I tried the F1 arms but the pins dug a groove in them and made my power valve feel wayyyy more sticky. I still have to try the newest version they sent me. But You can see the slight notch where the slide should be sliding.
I know of one person who had to buy a new cylinder due to the valve sticking.
The Shop
Number 11 on this diagram. That's the part that is sticky on my set up, that is the pin that ride along the power valve arm.
So if you remove everything but your controller flap(14), it's still sticking? Have you removed it completely and cleaned all the exhaust gunk off it with a wire brush?
I will post what he finds.
I am going to buy a new set and have them sent to Cryo Heat to have them micropolished and treated. This should help dramatically, I would think!
I have heard of some of engine builders taking a few .001 off the cover or REM finishing the PV parts. I sent my cylinder to Terry Varner. I will post what he finds.
Post any photos if you have them. Thanks!
I have a 16'150sx ...can you describe how the bike runs when the PV sticks ?
thanks , mark
It only takes a few minutes to take the pipe off and remove the power valve cover and watch the PV as you open the throttle. If in doubt pull the cylinder and check for smooth operation and if the valve is fully opening and closing. Not opening or closing by 1mm makes a big diference.
Ok , I will check it all out
I have noticed lately my 16' 150sx is running inconsistently
occasionally it staggers in acceleration & does not rev out completely like it used to
also seems to lag when accelerating off the bottom into the mid ..then takes off like a Banshee... lol
mostly seems to lack in torque when cornering ... almost like your foot got stuck on the brake pedal
jetting has not changed , temps don't change this behavior so I don't think its jetting
Thanks for the quick response
I will keep everyone posted.
Pit Row
The F1 arms have the potential to work better but he also had to smooth those out since they are a lot rougher than the OEM. So the F1 arms will need some cleanup work to function smoothly.
Thanks again to Terry Varner!!!
On another note: While I'm waiting for the cylinder I will be shimming the swingarm. The KTM's have too much tolerance between the swingarm and frame which causes a lot of vibration. Instead of fixing the issue KTM just made the motor mounts thicker on the 125 so they wouldn't break but the vibration is still there. You must add shims to eliminate the vibration. It's a pain but well worth it.
The shims take up the slack between the motor/frame and swingarm and frame. If you have ever worked on a jap bike you will notice the tolerance is very tight or hard to get the swingarm back in place. The KTM is easier to install but there is still a gap,
When you tighten everything the frame is only going to flex so much and you do not want to over tighten the swingarm nut to compensate.
I will post pics and shim sizes when I'm done with everything.
I have friends who managed and worked for the KTM factory teams and that is how I first found out. My friend had to even shim his kids KTM 85 a couple years back.
I mean think about the fact KTM made the huge motor mounts on the 16 125. That was due to the older 125's vibrating and breaking mounts.
Now the bind is gone & it runs much better .Strange
The first sets were water jet cut & manufactured from brass.
The next iteration would be stainless steel & cnc machined this should overcome the slight issues of the prototypes.
Might be slighty more expensive @ $85.
Any interest in this ?
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