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2011 KTM 300 XC-W downhill idle issue

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Hi Guys,

 

Been scratching my head with an annoying issue on my second hand 2011 KTM 300 XC-W and hoping someone out there can give me some advice.

 

Bike has lots of power and goes like a rocket. Steep hills are no problem but when I go downhill at say a 20 degree or more the engine has issues with idling losses power and cuts out. I can keep it running but need to keep the revs up which is a real pain. Soon as I hit flat ground power is back and idle is fine.

Same issue happens going over a obstacle etc.

 

My initial thoughts were with the carb and I started looking at the float level. Seems to be a common issue and is explained in https://thumpertalk.com/topic/864549-float-level-setting/ .

 

I’ve tried the recommendations but to no avail. Even took the carb to local KTM workshop and they confirmed settings look right. Jet is correct for my altitude.

 

Any ideas?

 

Cheers.

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Did you actually lower your float height? I see you know it's a common problem but I think I had to lower mine more than ktm recommend

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Did you actually lower your float height? I see you know it's a common problem but I think I had to lower mine more than ktm recommend

 

Yes this is what I thought of as well - This would make sense be as it's a downhill problem only.

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Thanks for the replies.

 

I've got the carb out at the moment - starting from scratch.

 

There are recommendations to set the float level lower stand KTM spec which is 16mm. The max distance the float on my carb can drop is 14mm. There is a plastic bar (part of float body) that prevent the float from dropping more than 14mm. See image for more detail: http://s14.postimg.org/68vgzh1b5/TT_Post_Pic1.jpg

 

I've got a couple of options:

 

1. Bend tang 1-2mm from 14mm to 12mm so the tang press against the needle without compressing the spring. Think I've tried this already but will again.

2. Remove the bar and go on standard spec based on 16mm drop and again bend tang 1-2mm to 14mm.

 

Any suggestions appreciated.

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I wouldn't remove or cut that bar you are talking about. Lots of these carbs work well with that attached so I'm sure you will be able to get yours to as well.

I would just bend the tang a bit so it shuts the fuel off sooner and not be to worried about taking real precise measurements.

I think your amount of drop is fine but as the floats rise they need to shut the fuel off earlier than they currently do by bending the tang the pushes on the needle valve up slightly.

I hope all this makes sense and is helpful to you. Sometimes it's hard to be real clear

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I wouldn't remove or cut that bar you are talking about. Lots of these carbs work well with that attached so I'm sure you will be able to get yours to as well.

I would just bend the tang a bit so it shuts the fuel off sooner and not be to worried about taking real precise measurements.

I think your amount of drop is fine but as the floats rise they need to shut the fuel off earlier than they currently do by bending the tang the pushes on the needle valve up slightly.

I hope all this makes sense and is helpful to you. Sometimes it's hard to be real clear

 

 

Good info ...lower float.  Stock setting to high.

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Hi guys, great info, just want to add some from my own experience. If adjusting the float level doesn't work, you need to (re)check the air screw. Mine was a little bit too much in and didn't allow enough air into the carb for the amount of gas when down the hill. Otherwise the bike ran great. After adjustin, the bike doesnt stall anymore and it runs as well as before, maybe even snappier.

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Hi Guys,

 

been a busy couple of months so haven't had time to provide update this post.

 

Happy to report problem is now fixed 👍 . Issue was with the float settings as suggested. Ended up bending the twang a lot more than I did before. The twang is bend around 4mm above the flat plastic bit where the float shaft slides into the carb body. With the float hanging all the way down the needle is now pushed up much higher than before. The needle body (sticking out of the shaft it pushes into) is around 2mm and this is with the twang just touching the needle spring - hope this makes sense.

 

For more detail see the photo below. Engine power is now much more instant and going down a 45 degree slope engine idles fine.

 

http://s10.postimg.org/6dvlg9zop/Float.png

 

Thanks to all those that offered suggestions - Cheers.

Edited by dvillijg
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After setting it up like this, did you measure to see what the float level is, by rotating the carb, making the float push the needle valve up to its seat, without compressing the spring loaded tit.?

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