FCR 39 throttle stuck open. AP?

I rejetted my bike and i was messing about for a bit to get the needle out. I used a screwdriver to hold the gate open from the top of the carb and pulled it a little hard. :prof: After that it would stay at wide open without any other input, and i could pull the curved armatures back far enough to take out the entire sliding gate assy, but i was blocked by the bike frame, so i left it.

To get the gate back down, i had to lightly hammer it, till it reached a certain point, then it seemed to pop into place and work normally. Put the bike back together and it had a high idle. Sure enough the gate did not seem to be fully closing onto the throttle stop. It seemed the ap screw was interferring with the throttle wheel, so after looking for other things, i took the screw off, same problem. Since it was getting dark i removed the entire carb. Upon further inspection the AP arms are not in the correct position. Its too far to the rear of the carb with the screw pointing into the throttle wheel.


Seeing this i tried to move the ap and it wont budge. :smirk: The Ap linkage will not move at all. Its supposed to right, so that it actuates the diaphragm in the bowl? Any help is appreciated. :smirk:

How far should the AP shaft move?

You are currently at its limit. Remove the needle, see if that is what is causing the hang. After it is out, if the system si still jamed:

I would remove the AP cover and pull the AP shaft dpwn, carefully unsnapping it from the cam. Next, remove the screws holding the slide to the throttle shaft. You will need to use an impact driver. Let the slide drop. Remove the throttle stop screw (the allen screw facing down, near the center of your picture. You should be able to rotate the throttle wheel further and have the lever re-engage the throttle wheel. Reverse to reassemble.

You will need to reset the AP timing. Loosen the idle speed so the slide is at the bottom. Set the gap to be .010" between the timing screw and the cam. Reset the idle speed just engough to see daylight through the carb.

Next time you want to do the needle, just remove the allen cap, remove it and use needle nose pilers to slide the needle out.

what a perfect explanation ^^^

the system wont let me give you anymore gas :smirk:

Thanks! :smirk:

William1, thank you so much. I got it back to working right but it looks like my float seat seal failed when i took it out to clean the screen (deduced from another post of yours). I learned a bunch just taking the carb apart. Ive been intimidated by carbs until now (fuel injection kid) but their operation is not so ethereal now and IMHO its rather ingenious.


Edited by snailspool

The oring is available at many KTM dealers and a places like Cyclewearables.com

And you are very welcome. I appreciate the kind words.

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