[![Yiben 50cc Carby port identification

]1]1I am trying to get this scooter going after sitting in a shed at a nursing home for 4 years.

I have started by cleaning the fuel tank, installing a new fuel filter, dismantling & cleaning the carby then putting it all back together as I found it, however there are 2 fuel line ports that were not connected to anything. The 1st at the top left side of the carby body just on the left side of the automatic choke ( The fuel line is connected to a port to the right of the auto choke)

The 2nd at the bottom of the carby beside what I would think is the Drain plug. It appears to be referred to in parts diagrams as a hose overflow but I can’t see what it should be connected to. I have searched on line but I must be looking in the wrong places so I hope someone can help

  • 1
    Make/model/year info would go a long way towards helping you, plus some pics. Dec 28, 2015 at 12:58
  • Yes, make/model/year please. If you can post a picture of your carb, that would also be beneficial. If not, make/model/year at a minimum. Thanks! Welcome the Stack Exchange. Cheers!!!! Dec 28, 2015 at 17:34
  • Sorry I thought I had the model in the header it is a Yiben YB50QT 50cc. As you can see I am still trying to find my way around this site so I will also attempt to add a photo of the carby
    – Ken
    Dec 29, 2015 at 20:04
  • I saw the url of your pick when I went into edit mode on your post and fixed it. Dec 29, 2015 at 20:08
  • Thanks for fixing my photo of the carby. What did I mess up so that it didn't post. That said does it make it any easier to identify where I should connect the hoses
    – Ken
    Dec 30, 2015 at 7:35

2 Answers 2


The two hoses in question can be identified by using a can of carburetor cleaner with the red hose attachment and squirting into the nipples for the hoses to see where the fluid emerges.

  • I suspect the nipple on the top of the carb by the auto choke could be a vacuum line. This is frequently where they are placed. The vacuum line may need to goto a petcock on the gas tank if you have a gravity feed fuel mechanism and no fuel pump. This is a guess as you have not posted your make/model/year of the scooter. If you squirt some carb cleaner into that, and I am correct, you will see fluid (carb cleaner) emerge from the head side of the carb between the venturi opening and the throttle body. That's the location for vacuum to be created in the carb. If it does not emerge from that location, please post as a note with additional info and I will edit this post to reflect the correct info.

  • The hose on the float bowl is a float drain tube. You can attach a hose to that and route it with any other lines from your fuel tank that emerge at the bottom of the scooter. It does not attach to anything.


  • Sorry I thought I had the model in the header it is a Yiben YB50QT 50cc. As you can see I am still trying to find my way around this site so I will also attempt to add a photo of the carby
    – Ken
    Dec 29, 2015 at 20:04
  • See my post above Dec 29, 2015 at 20:08
  • 30 12 15.JPG I am still trying to up load a photo
    – Ken
    Dec 30, 2015 at 19:55
  • Try a different browser. Dec 30, 2015 at 20:36

It would be nice to see some pictures of your carb, because each carb is different.

But let's see...

There's usually a drain screw at the bottom of the carb, which allows to drain accumulated water and/or fuel from the floating chamber. There's typically a port for a hose, which just leads to the ground. I.e. this hose is not connected anywhere. If the scooter doesn't start after a long while sitting around, a first try is to completely drain the carb. It will fill up with fresh fuel from the tank, which will burn better.

The upper part of the carb usually has at least two ports: One fuel line and one vacuum line. The fuel line leads directly into the floating chamber. If you disassembled the carb, you may have noticed a small pencil-like stud, which is the valve regulating the fuel level in the chamber. This stud closes the fuel line when the level is high enough.

However, this valve isn't strong / tight enough to prevent flooding the motor when the scooter is sitting around. Therefore, there is another valve at the bottom of the tank:

enter image description here

By applying vacuum to the lower port, the valve opens and fuel flows out of the upper port. This vacuum comes from the intake of the motor, and a port for this can often be found at the carb. This port usually sits in the middle of the "pipe" near the outlet of the carb.

Sometimes, there are even more hoses. For example, two for carb heating if the scooter is water-cooled or one with small diameter for oil in case of a two-stroke-engine.

So, if this doesn't help, please post some pictures, and if you have, drawings!

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