ORIGINAL: j.duncker
When checking the fuel line remember to look at the clunk line in the tank. If that has a hole you will get the symptoms you you describe.
Very true.
If it runs fine when the tank is full, and only does it at 1/4 tank or less, my guess is either a hole in the clunk line, OR, it's very possible you're getting fuel foaming, but only when the fuel reaches a certain level.
Another possibility is that you could be just running out of fuel. You may have 1/4 tank, but that's not much. Any number of things could be keeping the fuel from reaching the carb.