Fuel coming from pipe and carb overflow

[rmpurps]

Hi all,

I've got a 2016 KTM 125SX which won't start after sitting for a good few months.

The symptoms are -

- Fuel floods out the overflow pipe for the carb.

- Fuel spits out of the expansion chamber where the exhaust meets the engine.

- Plug is soaked in fuel

The above suggests to me it's a carb issue, particularly the float. So far I've taken the carb off and checked a sticky float which all seems fine and clean. Other things I'm going to check are the fuel cock and reed block. I'm thinking I'll blow out the jets and take the pipe off and make sure it's not full of fuel also.

Before I go chasing down a rabbit hole, has anyone experienced the same and have an answer?

[mlatour]

Your fuel / fuel system may be contaminated by debris, preventing the fuel inlet needle from sealing.

[raymo2.0]

I left my bike set for a few weeks with the petcock on, Filled the engine and exhaust pipe full. I tried to pump it out with the pipe still on but no start. When I pulled the silencer gas ran out that is how much fuel was in the system. I then pulled the pipe and it was full of gas mix also.
 Pulled the silencer and pipe, pumped the engine till there was no fuel coming out, put a new plug in and off I went. I did pull the carb to make sure the seat was clean.

 

[rmpurps]

14 minutes ago, raymo2.0 said:

I left my bike set for a few weeks with the petcock on, Filled the engine and exhaust pipe full. I tried to pump it out with the pipe still on but no start. When I pulled the silencer gas ran out that is how much fuel was in the system. I then pulled the pipe and it was full of gas mix also.
 Pulled the silencer and pipe, pumped the engine till there was no fuel coming out, put a new plug in and off I went. I did pull the carb to make sure the seat was clean.

 

Did you have fuel pissing out the carb too when you turned the fuel on?

[ss-racing66]

17 minutes ago, raymo2.0 said:

I did pull the carb to make sure the seat was clean.

Its very likely the both of you have a worn out fuel inlet needle, fuel is not supposed to keep flowing into the carb (at all) once the float gets to the proper level.

[Fairweatherider]

1 hour ago, ss-racing66 said:

Its very likely the both of you have a worn out fuel inlet needle, fuel is not supposed to keep flowing into the carb (at all) once the float gets to the proper level.

^^Check this first. As well as the previously mentioned debris clogging that rubber needle seat. 

Something leaking out of the pipe? My son thought it would be funny to pee down the silencer of his little brother’s yz65. Make sure you haven’t been pranked by your buddies. 

[RichieGoatGruff]

41 minutes ago, Fairweatherider said:

^^Check this first. As well as the previously mentioned debris clogging that rubber needle seat. 

Something leaking out of the pipe? My son thought it would be funny to pee down the silencer of his little brother’s yz65. Make sure you haven’t been pranked by your buddies. 

Bet that smelled good....

?

[rmpurps]

Update: 

 

So far I've taken the carb apart 3 times. I adjusted the float one way which still made it leak so I went back the other way and it's still leaking. To test it closes I put a pipe where the fuel comes in and blew into it, then tilted the carb until no air would flow through which works fine so it seems to close. I can't understand why fuel will still flow through it when the needle is closed. The angle in the book says 60° but even passed that it makes no difference. I would expect it to just stop any fuel going through past that angle anyway.

 

Any ideas?

[RichieGoatGruff]

Does the float float? Sometimes they leak...

[rmpurps]

20 minutes ago, RichieGoatGruff said:

Does the float float? Sometimes they leak...

Yep it floats. No leaks from the float bowl either

[RichieGoatGruff]

Only thing left is the needle/seat... Post pics.

[rmpurps]

Inlet needle and seat look fine too

[GKRContracting]

There’s not much else it can be other than float or needle and seat. Looking at your needle, there is a spring loaded plunger in the back of the needle. Is it moving? It may be stuck. It’s purpose is to prevent the bowl from overfilling due to “float bounce” in off road situations. As the float pushes the needle towards the seat the first contact occurs with the plunger out and that is where you set float level. From that point the float can travel a little further as it compresses the plunger spring. This spring loaded effect keeps the needle on the seat even in rough terrain. Check that the plunger is moving freely and set the float level based on just where the needle contacts the seat. (All this is based on you have this style of needle, most do but not sure on your specific bike model)

If you have tried higher and lower float settings and neither made any difference it’s likely not what I have suggested above.  I would look for some debris stuck in the seat  Your needle tip looks good but it will not seal if there is a piece of junk on the mating surface of the seat. Most needle and seats are replaceable and available in a rebuild kit  

Hope this makes sense. 
GKR

[KillerK]

You may be getting a step in the needle. You can see it faintly in your photo. Run your fingernail across it and see if you can feel anything. Polish the seat with a q tip. I think people use toothpaste as a mild abrasive on the q tip.

[ThumpaGreg]

With the float bowl off, connect the carb to fuel and turn it on. Check that the float will shut off fuel flow if you gently hold it up with finger pressure, which of course it should do. If it won't, there is a problem with the float/valve. This will also let you see whether or not there is some other strange reason for fuel getting into the carb.

[DOSHOW]

+1 ThumpaGreg just said what I was going to try.  I just went thru the same problem you are except on one of my old YZ's.  I could barely feel a scratch on my needle.  Replaced it and now works like it should. 

[rmpurps]

I've left it for the day now but the last thing I tried was as you guys said, taking the bowl off and connecting fuel up to see if the float stopped fuel flow using my fingers. It did and also showed no other signs of any other leaks from odd places.

Tomorrow I'll give it another good clean on the seat and needle and see how it goes. If no change I'll order a new needle and hope it solves the problem. I imagine at this stage it'll be something so small it's hardly noticeable.

Thanks for the advice so far all! Will keep this thread updated once solved for future reference to others.

[Randy300XC]

Are the vent lines the same as stock? The stock setup has the vent lines that go up and over the carb, then back down and under the bike. Did you modify and lines?

[Eli T]

Is the float adjusted right? 

[kjman2]

there is also  a o ring  around the seat that could be leaking I had it happen on my 300 that was one year old at the time,