I've got a small engine (11 HP B&S) that has a gravity-fed fuel system, i.e. there is no fuel pump, simply a fuel line between the carburetor and the fuel tank. If I look at the short (~2-3") piece of transparent fuel line between the filter and the carburetor, I can see bubbles (rather large ones, maybe 1/2 the diameter of the fuel line) traveling from the filter into the carburetor.

Is this an indication of a leak in the line, the filter, or one of the connections? Should I be concerned, or is this normal?

I'm also experiencing a loss of power when the engine heats up, and I'm wondering if the bubbles could be related...


Could be a possible air leak. This affects your mixture, and would likely be the cause of the problem. Have you tried replacing/tightening the clamps on the hose?

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  • An air leak in a gravity-fed system? If there were a leak, wouldn't gas leak out, instead of air leaking in? There's no fuel pump here creating a vacuum in the fuel line. – Mark Jun 9 '11 at 15:24
  • Small enough for air, and not fuel. I guess you could be correct though, but doesn't the carburetor create a vacuum? I have never messed with them, but do recall the engine creates a vacuum when it goes in the down stroke. – FossilizedCarlos Jun 11 '11 at 19:34
  • The bubbles we're talking about are definitely large enough to be indicative of a leak big enough for gas to get out. – Mark Jun 13 '11 at 16:16

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