520 Weak Throttle Return Spring, Stuck Throttle

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#1
:think
If my bars are turned to the right, the throttle sticks open. Not a good thing Martha. Took the tank off. Checked the cable routing. Even took the throttle grip off the bar. When there is enough of a bend in the cables, the throttle return spring cannot close the throttle. While I've marveled at the light throttle pull, I'm non-plussed about this discovery. I spent several hours, fiddling with cables, to make sure something wasn't bound up or kinked. It isn't. Proof of this is the very light effort required to twist the throttle open. The problem on mine, is the return spring is simply not strong enough. I suggest you check yours carefully.
 

Jaybird

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#2
Have you disassembled the throttle mechanism? I had some problems with my throttle, but after I cleaned the gunk out and re-lubricated the mechanism, it was fine. Maybe you screwed the spring up while jetting? Also, look to see that the spring retainer (under carb top cap) is seated properly. It has a notch in it and if it's not seated properly it can cause problems like yours.
 
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#3
Thanks for advice Jaybird

Here's an update. Called the dealer I bought from. He's out of state. Though not unpleasant, he was insistent nonetheless that my cable routing was wrong. So I checked the book, routing was correct. Called him back, he gave me direct number to KTM to see if it might be a known problem. Haven't called yet, but on re-examination found an ever-so-slight kink in the area along the frame backbone where it runs under the tank. I carefully massaged this out with the flats on a pair of needle nose pliers. This helped, but throttle still would not return completely if bars turned fully to the right. Against my better judgement, I decided to lube the cables. Disconnected them from the throttle pulley, and checked the mainspring at that time, which was clean and properly installed. Held the cables upright, and used a dropper to drip in some Mobil 1 5W-30. Allowed 10 minutes for the oil to drip down via gravity. Then operated the cable. Reinstalled to the throttle pulley, adjusted the cables, and it seems to be working fine again. These appear to be old style cables, so I don't think there is any harm in lubing them. I had no alternative regardless. A 520 with a sticking throttle is not good.
 

Jaybird

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#4
Sounds like you've pretty much solved your problem. I don't like to use thicker oils to lubricate cables. When you have the throttle assembly apart next time, try using a can of silicone or teflon spray lube. Just use the little tube that connects to the nozzle and spray it down your cable. I like to take my cable loose from the carb before I do this, but it probably won't hurt just to spray and go. Make cable lubing part of your ritual.

Good Luck!
 
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#5
Okay. I'll try that next time. Silicone will be better for not attracting dirt. The spray tube with aerosol can good advice too. Some cables, I guess mainly on GM automotive applications for throttle bodys, are advised against lubing. But they are treated internally. I think teflon lined. These old style cables apparently still benefit from lubing. It's something I'm going to watch out for. Don't want stuck thottle putting me in the same zip code as Dale Earnhardt.
 
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#6
You know this is a TWO way cable system, if it dosen't "spring" shut...you can roll it shut...there by avoiding joining Mr. Earnhardt.:eek: