Gas leaking from carb top vent tube

[Deleted member 97405]

The reason the fuel is coming out the vent tube is because the bowl of the carb is overflowing. The vent tube is a port that goes directly to the bowl of the carb. When the bowl overflows, the fuel pushes out the vent tube rather than all going into the engine intake. You definitely have an issue with that carb inlet. The fuel pump is a low pressure pump and will not overpower the float needle unless there is a problem there, i.e debris in the inlet. When my sister's tractor had the same issue, I had to replace all the parts listed above. All it takes is a microscopic piece of debris to keep that inlet needle from properly stopping the flow of fuel. That ethanol is crap, and if your system is contaminated, the only way to correctly fix it is to replace all the parts. There is no way to thoroughly flush a contaminated fuel pump unless you want to take that chance and have to pull your carb many times to clean it. On a side note, I have had Chinese carbs leak internally right out of the box. Could be you just have a carb issue now. The metal the carb is made out of is porous, meaning gas will find its way through it. The carbs are coated with a sealer invisible to the naked eye. This is why you don't soak a carb in solution too long because it eats that coating off. Chinese carbs are inferior, and the coating isn't as good as OEM, therefore, it may be leaking for that reason as well. Over 20+ years, you see a lot of things, but with this system, I've only successfully fixed it by following the post I posted above. Otherwise, this issue could plague you until you're sick of the tractor. Good luck.

 

[Hammermechanicman]

If you can do a cylinder leakdown test. Especially check intake valves for sealing properly. A bad intake valve on a twin can cause poor running and fuel to be spit out of the carb.

 

[Deleted member 97405]

If you can do a cylinder leakdown test. Especially check intake valves for sealing properly. A bad intake valve on a twin can cause poor running and fuel to be spit out of the carb.

This will cause fuel to spit out the throat of the carb and soak the air filter. He's not having that issue. His fuel is coming out the vent tube. Good input though.

 

[PTmowerMech]

Well, this thread didn't solve anything. I'm having the same issue. Everything new, except the fuel pump. I get what @Rivets said, if the carb is getting fuel, then the pump must be OK.
But then again, this is a mechanical fuel pump and since this vent tube apparently goes straight though from the float bowl to the vent, then I can see how the pump over over-pump.

Some guy on a video said he adjusted his float so that it didn't drop down as far. Which made no sense to me. I think he just got lucky. But did say that he still has the same problem with the new carb. And that's the float he adjusted. Then it shows him mowing and it running and cutting fine (for like 10 minutes)

 

[PTmowerMech]

Problem solved (for now). I did a few things, so I'm not quite sure what actually solved the problem. But here's what I did.

1. Removed the new carb and cleaned it.
2. Used the float from the old carb. It seemed to sit as level. But when you turn it right side up, it didn't drop as far. So my thinking is, the needle could've been binding and not closing all the way. This one has that wire hanger that keeps it attached to the float.
3. Since the fuel pump was old, I put a filter between it and the carb, just to see if there was any thing coming from the pump. And in deed there was. After about 20 minutes of running it, there were a few small specks of something caught in the filter. Now there's a filter before the pump and one after.
4. I put a piece of 2 cycle fuel line from the vent down through the frame, just in case it started overflowing again, it wouldn't be close to the muffler.

After all that, and getting everything back on, the engine surged real bad. So I opened up the mixture screw and leveled it out. I did have some trouble getting the choke adjusted, But I think I got that working now.
And lastly, I set the high idle about about 3700 RPM.

So if anyone else has this problem, and used an amazon carb ($25 vs $300). and it still does it, you might try using the old float and two filters.

 

[slomo]

From what I've seen on Chinese carbs, if you go through the parts, make sure they do what they are supposed to do. And like you did substitute parts when needed. Most of the time you can get them to work if they don't work out of the box.

 

[PTmowerMech]

From what I've seen on Chinese carbs, if you go through the parts, make sure they do what they are supposed to do. And like you did substitute parts when needed. Most of the time you can get them to work if they don't work out of the box.

Right.

It was in all the forums I read on this carburetor, with so many people trying so many different things. The one thing that stuck in my head was a video of some guy who I could barely understand, who didn't even know what the parts of the carburetor was. He mentioned something about bending the ear of the float so that it didn't drop down too far. At first, that made no sense, because I was thinking that it didn't matter how far the float dropped, as long as it came back up and sealed the needle when the bowl was full.
But then another guy (I can't believe I'm about to repeat this).... He took some aluminum polish on a cue tip, put the cue tip in a drill and polished the inside wall of where the needle rides. This, believe it or not, made his needle slide in and out very easily. It's probably made the ID a tiny bit bigger also.

Add those things with what @Rivets (and others) said about the only thing that could be causing the problem is the needle not seating, and KA BOOM,

 

[bertsmobile1]

If you are catching crud after the fuel filter then some thing between it and the carb is on its way out
As you know you do not need much crud under the float needle to cause it not to seat
A little tool you might consider making is a dead solenoid , guts removed and piece of plastic tube attached
Tie the tube off so it is upright then you can see what level the float needle actually allows the bowl to fill to .
It is a std tool for British bike techs who try to tune Amal concentric carbs which seem t come from the factory with random float heights

 

[PTmowerMech]

From what I've seen on Chinese carbs, if you go through the parts, make sure they do what they are supposed to do. And like you did substitute parts when needed. Most of the time you can get them to work if they don't work out of the box.

I'm in the process of building me another work bench, that's going to include another carburetor test cradle. Where I can hang a carb that's attached to a fuel tank, to check it for leaks or overflow before installing it. Those are pretty handy with todays amazon carbs.
I gotta say, this one, like most others I've gotten from Amazon have been OK. I know they get a bad rap, but honestly I not gotten a bad 4 cycle one in a while.
The last 2cycle carb I bought, I thought was junk. But it turned out to be the throttle cable was not routed right.