I agree with above posts. The line in the tank softens up over time allowing it to bend more easily. Losi has 2 different fuel lines. One is light blue and the other is clear. I don't even bother with the light blue stuff. It is way too soft for inside the tank. Some tanks come with the blue in them and I usually replace it with the clear line immediately. It can also happen if your clunk is not positioned in the tank correctly or if the line pulls out some during a race. You want the clunk towards the back of the tank in the little indentation. Not too far back as to where it gets hung up on the back tank wall. Best way to make sure it is in the right place is to shake the tank around a bit with it out of the truck to make sure it isn't getting caught on anything.