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 Post subject: KTM carb overflow issue
PostPosted: Tue Aug 29, 2017 4:53 pm 
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Dirt Shark
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Location: Acworth, Ga.
This one has me stumped.

My son's 2012 KTM 150 XC has a strange issue. The carburetor will overflow gas out of the tube connected to the bowl. Has to be the float needle not seating or the float height not set correct? Nothing strange so far.

But........ it only happens after it sits for a few days. When we first ride, it will do it. We run the bike a minute or two with the gas off and the it's fixed for the rest of the day. After it's "fixed for the day" we can stop for long periods of time with the engine off and it won't overflow.

I have taken the carburetor apart 2 times and cleaned it to no avail. I just replaced the float needle and it still does exactly the same thing.

Interested in your thoughts on this one. ::popcorn::

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 Post subject: Re: KTM carb overflow issue
PostPosted: Tue Aug 29, 2017 5:22 pm 
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KTM GURU
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That is an odd one, but I bet it's something very simple. Make sure your floats are not rubbing anything on their way up and down, also make sure you do not have any 180-ish degree bends in the fuel line. And of course it goes without saying that the muffler enflatulator needs to have the nitrogen pressure checked.

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 Post subject: Re: KTM carb overflow issue
PostPosted: Tue Aug 29, 2017 5:42 pm 
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Dirt Shark
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Hmmmm, I get the thought that the float could be dry and after it gets gas/oil that it could lube it just enough to properly work and the enflatulator pressure theory, but 180 bend in the fuel line? What's the idea on that one?

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 Post subject: Re: KTM carb overflow issue
PostPosted: Tue Aug 29, 2017 6:17 pm 
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S.Anderson wrote:
Hmmmm, I get the thought that the float could be dry and after it gets gas/oil that it could lube it just enough to properly work and the enflatulator pressure theory, but 180 bend in the fuel line? What's the idea on that one?

I have seen some strange carb issues now and then with fuel lines routed oddly. A 180 degree or more "U" in the line, especially if the U is like a sink P trap, can air lock and make the floats drop low in the float bowl where they might rub or hang just as the air lock releases and fuel dumps in. You can get an overflow situation until the floats jiggle free.

It's something simple. You just haven't found it yet. ::cheers::

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 Post subject: Re: KTM carb overflow issue
PostPosted: Tue Aug 29, 2017 6:27 pm 
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I'll assume you've verified the floats are good and don't have any fuel in them?

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 Post subject: Re: KTM carb overflow issue
PostPosted: Tue Aug 29, 2017 6:50 pm 
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Dirt Shark
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ScottGreer wrote:
I'll assume you've verified the floats are good and don't have any fuel in them?


I honestly have not. I didn't think too deep into it until the needle valve didn't work.

I'll check that but it seems like I'd have a an opposite problem if the floats were not buoyant.

Love bouncing ideas and thoughts.

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 Post subject: Re: KTM carb overflow issue
PostPosted: Tue Aug 29, 2017 6:57 pm 
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Dirt Shark
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On second thought Ithe problem would occur if the float weren't buoyant but it wouldn't explain why it works after the first few minutes.

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 Post subject: Re: KTM carb overflow issue
PostPosted: Tue Aug 29, 2017 8:39 pm 
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All vent lines clear, including tank cap?

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 Post subject: Re: KTM carb overflow issue
PostPosted: Tue Aug 29, 2017 8:43 pm 
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Its probably a long shot, but I found a trick on youtube that fixed my 2011 250xc carb when I was having a similar issue. I would park the bike after riding and next morning come out to find it had been dripping fuel from the vent line.

The probem was the float valve seat was either corroded or scratched. I put some metal polish on a qtip and put it in a dremel. Then polished the valve seat, probably went through 10 or so qtips. I didnt have much faith, but it ended up working.


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 Post subject: Re: KTM carb overflow issue
PostPosted: Thu Aug 31, 2017 1:39 pm 
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Location: Athens, Ga.
Steve, as discussed Sunday, I am still having the same problem also. Replaced the float valve and same problem. Set the float level and even verified with Craig's "2:00 o'clock" method. I'm thinking kbro45 is onto something. Something scarred on the valve seat or maybe some trace debris on the surface. On mine nothing I could detect visually. I did find tell tale signs of a few small black particles in the float bowl. They smeared and cleaned off with a Q tip, like little bits of grease. Are you guys running some race fuel mixed with ethanol free? We are using a 3/2 mix, 90 octane/110. Could the race fuel have an additive that is melting the inside rubber of the fuel line?
Anyway, I'm gonna try some Sea Foam in hope that it might clean the valve seat.


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 Post subject: Re: KTM carb overflow issue
PostPosted: Fri Sep 01, 2017 6:25 am 
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Dirt Shark
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We use regular high octane pump gas.

What is baffling is that it corrects it's self for the remainder of the day. To me, that means something must change and *in my mind* it must have something to do with the float not being able to move all the way up. Once it does, the needle seems to do the trick sealing.

Our method:

Turn the gas on at the beginning of our ride..... it 80% of the time leaks.
Turn the gas off, crank the bike for approximately one minute.
Turn the gas on, and check it. Most times, this corrects the problem until the next ride a week or so later. ::screwy::

At the end of the day, we always turn the gas off. Something happens during this time. Maybe the gas evaporates and the bowl is dry? I know the gas has to evaporate enough to cause the issue when we first ride again.

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 Post subject: Re: KTM carb overflow issue
PostPosted: Fri Sep 01, 2017 7:06 am 
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Roger, do you store your bike on the kickstand or upright?

A new idea I had. We store ours on the kickstand until the next ride. What if the float slightly slides to the left (downhill side) as it sits for a while. The float slightly drops due to the gas evaporating and moves slightly to the side causing the issue until it's operated upright again?

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 Post subject: Re: KTM carb overflow issue
PostPosted: Fri Sep 01, 2017 8:20 am 
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A tap on the bowl should fix that. Almost sounds like you have some type of pressure acting on it.

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 Post subject: Re: KTM carb overflow issue
PostPosted: Fri Sep 01, 2017 8:31 am 
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Do you store the bike with a dry carb?

If you do, I'm thinking the little rubber nipple on needle may get a bit dried out and harden a bit, which won't let it seal the fuel port when the float is up. Then after soaking in the fuel for a while it gets softer and begins to make the full seal.

Just some thoughts.


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 Post subject: Re: KTM carb overflow issue
PostPosted: Fri Sep 01, 2017 9:35 am 
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mog wrote:
A tap on the bowl should fix that. Almost sounds like you have some type of pressure acting on it.
Pressure . . . . now there's an idea. ::geek:: Do you have one of those one-way check valves on the gas cap?

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- c bob

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