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dec699

Carb overflowing

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Haven’t had any carb issues in the last 3 years since I purchased my 2009 KTM 300XC with Keihin PWK carb. I recently replaced the throttle cable, but only rotated the carb to do so and it looked pretty level when the install was complete. While out on the trail the other day, I dropped the bike.  When I picked it back up, fuel kept overflowing through what I believe is a vent tube.  I tried tapping on the bowl to get the needle to seat, but no joy.  Carb still looked level. Leaning the bike to one side or the other didn’t have any noticeable change.  Couldn’t get it to stop overflowing, so I shut the petcock off and coasted back downhill to the truck.  It seems as though I’ve got a needle/seat/float issue.  I might even have a plugged overflow?  Any advice on what to look for before I get in there.  My finger is on the line where the fuel was overflowing from in the pic.  Thanks.

 

 

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If it's overflowing, you are on the right track.  Needle valve is stuck open for some reason.  Maybe just getting dirty, or you may have a chunk of dirt holding it open.  The rubber tip could be bad, or the seat could be getting rough.

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4 hours ago, weantright said:

Get a new needle and seat along with an inline fuel filter.

Seat isn't replacable on this type of Keihin.

Yes I know, some specialists can replace it but as it worked well before the OT changed the throttle cable it is probably just a piece of dirt in the float valve or the valve needle or the float have tilted and got stuck. Easy fix.

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Take the fuel line off at the petcock and blow air into the carb. Either just by mouth or with a bicycle air pump, nothing high volume. Fuel will come out of the vent lines and that’s ok. Do it a little longer after the fuel stops. Hook it back up and test it. This can sometimes remove any debris from the valve seat and float bowl. 

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I agree with what the others say about dirt getting in between the needle and seat. It's not uncommon for fuel to leak out of the upper air vent lines when the bike is on its side. However, once the bike is righted the flow should stop, if not the flow should come from the drain line on the bottom of the fuel bowl. If it continued to flow from the upper air vent line you have an obstruction in the fuel bowl drain line or the brass tube inside the fuel bowl is clogged and should be cleared.

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My first guess would be a tiny bit of crud, from anywhere in your fuel system, is lodged in the float needle seat.  You can try to flush it by removing the drain screw in the bottom of the bowl and opening your petcock for a bit.   Fuel will go everywhere unless you can capture it somehow. 

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There’s no easy way to remove the bowl with the carb on, correct?  When I replaced the throttle cable, I was only able to rotate the carb maybe 1/4 turn. If not, I assume it helps to remove the subframe bolt and rotate the air box out of the way.

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depending on how willing you are to keeping the bike well maintained and good looking if i were you i would use a ultrasonic cleaner and get a carb rebuild kit its about 20-30 for the kit and a ultrasonic cleaner 2.5l ones for 80 works fine 3L are better. If you dont want to invest in a ultrasonic cleaner boiling water-soap pressure washer small toothbrush and air compressor work good too. (thats how i did my first carb)

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A friend of mine bought a cheap aftermarket float valve for his old YZ, it took about a month for it to start hanging up on the seat. He literally shaved some of the rubber with a razor blade as a temporary fix for the day.  He bought a Keihin float valve, no more problems.  Don't waste your time and money on cheap carb parts.  

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My son had the same trouble on his 2016 250sx. He ‘rebuilt’ the carb by cleaning, then used most of the parts from a carb rebuild kit after, and set the float level. After that he still had dribble from the overflow. He then cleaned the filter on the petcock that is inside the tank, then replaced the fuel hose with the yellow fuel tubing used by landscapers in their equipment, and the final thing was he blew air through the carburetor fuel inlet tube to flush out the bowl. Fixed. 

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28 minutes ago, Randy300XC said:

My son had the same trouble on his 2016 250sx. He ‘rebuilt’ the carb by cleaning, then used most of the parts from a carb rebuild kit after, and set the float level. After that he still had dribble from the overflow. He then cleaned the filter on the petcock that is inside the tank, then replaced the fuel hose with the yellow fuel tubing used by landscapers in their equipment, and the final thing was he blew air through the carburetor fuel inlet tube to flush out the bowl. Fixed. 

you can also use inline fuel filter to futher prevent future carb realted problems

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4 hours ago, Triple Nine Motorsports said:

you can also use inline fuel filter to futher prevent future carb realted problems

We’re pretty sure the ethanol in the fuel was dissolving the stock fuel line from the inside. It looked strange and was softer than it should be. 

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On 10/14/2020 at 5:12 PM, Triple Nine Motorsports said:

depending on how willing you are to keeping the bike well maintained and good looking if i were you i would use a ultrasonic cleaner and get a carb rebuild kit its about 20-30 for the kit and a ultrasonic cleaner 2.5l ones for 80 works fine 3L are better. If you dont want to invest in a ultrasonic cleaner boiling water-soap pressure washer small toothbrush and air compressor work good too. (thats how i did my first carb)

I’ve got an ultrasonic cleaner. It works wonders on lawn equipment carbs. I think I can get it to clean everywhere if I rotate the carb.  I noticed the rubber boot between the carb and the reed cage is starting to crack. I’m gonna pull the carb anyway so that I can replace the boot and the reed valves while I’m at it.

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Just now, dec699 said:

I’ve got an ultrasonic cleaner. It works wonders on lawn equipment carbs. I think I can get it to clean everywhere if I rotate the carb.  I noticed the rubber boot between the carb and the reed cage is starting to crack. I’m gonna pull the carb anyway so that I can replace the boot and the reed valves while I’m at it.

Oh nice what kind did you get?

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“Dare Flow” 2.0L unit with a 200W heater; got it on Amazon. Regardless of where you shop, they’re all identical and they’re all made of Chineseium.  I paid more than I wanted to for this unit, but it has a bigger heater than almost any other of it’s size. The heat is key and I didn’t want to wait forever for the solution to get up to temp.  I had to covert F to C so that I know what temp I’m dealing with, but so far I’m happy with it. Everything I’ve put in it has come out nice and shiny

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