So the title is kind of generic, but I am facing a bit of a weird situation. I am going to explain it first, but I also have some pictures at the end that might help.

I have bought a cheap 2 stroke engine that was completely seized and gummed up. After fixing all the other problems I managed to get the engine running on ether. I had cleaned up the carburetor and managed to get all vents cleaned up. It does not use a traditional carb, since it does not have a float bowl, it is directly fed from the gas line and has practically no jets/valves. It has a suprisingly large air intake.

After everything was cleaned up I hooked it up to the gas tank and noticed that fuel does not really get out of the tank to the carb even if the fuel shut off is opened. I unplugged the fuel line from the carb and fuel started flowing immediately. Naturally fuel not getting to the carb could either mean there is a vacuum leak or something is blocked. Since fuel is not even going to the carb by gravity (the fuel tank is higher than the carb) I was assuming something is blocked. First guess, the fuel tank vent is not working. I removed the cap from the gas tank, no change, so guess the fuel vent on the top of the fuel cap would not help either.

Now this is where it gets interesting. I plugged the fuel line into the carb and removed it from the tank. I fed some fuel using a bottle into the fuel line and I could see it move freely into the carb. The engine works without any issue and runs until the fuel in the line is used up. So apparently nothing in the carburetor is blocked I would assume.

So I am in the following situation:

  • Fuel does flow through the line when it is only connected to the fuel tank (with or without cap)
  • Fuel does flow through the line when it is only connected to the carburetor
  • Fuel does not flow through the line when it is connected to both the carburetor and the fuel tank

I am a bit confused whats going on, obviously none of the components is blocked, the vacuum is also fine or it would not run perfect when it is not connected to the gas tank. What could cause this?

Below are some images showing the carb. It is still showing the old gummed up fuel line and filter that I have replaced by now, so that is not it. I forgot to take an image with the air filter off, but there is nothing else there except the air cleaner.

enter image description here enter image description here

  • Did you have that fuel filter included in each of your experiments?
    – HandyHowie
    Commented Jun 19, 2022 at 22:26
  • What is the make and model of the engine?
    – HandyHowie
    Commented Jun 19, 2022 at 22:26
  • I ran everything without the filter. I know the manufacturer is AS Motor, serial number 04433002. Seeing as the plate with the serial number says "west germany" I assume it is quite old. I am trying to find more information. Commented Jun 20, 2022 at 18:08
  • Can you add a photo of the whole engine from above?
    – HandyHowie
    Commented Jun 20, 2022 at 18:35


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