I hope someone can help me resolve this frustrating situation.

My lawnmower (Briggs & Stratton Max engine) is not starting and it has had problems starting/staying on before this. I followed others' advice to clean the carburetor and change the spark plug, but it is still not starting. Now, I notice gas is leaking from the carburetor cup around the rubber gasket area opposite the bolt. The cup does not feel snug and has some wiggle room which makes sense why it's leaking, but as I put it back together the way I disassembled it, I cannot figure out what the problem is. I have tried reseating the gasket and tightening the bolt several times but each time once I open the fuel line the cup begins to leak again from that same spot.

So now I have a bigger problem that needs to be resolved first, but:

  1. What is the problem and how do I fix the leak?
  2. How to I get the engine running again? The new spark plug supposedly comes pre-gapped to the specification my mower requires so I'm not sure if that is the issue. The gas in the tank is anywhere from 1-6 months old. Oil level is good.
  • There is usually a gasket between the bolt and cup. Is that gasket present? If its missing it may cause the cup not to seat all the way.
    – vini_i
    Commented Mar 27, 2016 at 13:51
  • as i mentioned, the gasket seemed to be in place and i tried reseating it several times. it did not move when i removed the cup,
    – Jon
    Commented Mar 27, 2016 at 14:21
  • even with the bolt removed the cup seems to wiggle slightly. if anything, the bolt gasket would only add to the room, not subtract from it
    – Jon
    Commented Mar 27, 2016 at 14:48
  • There are two gaskets. One between the cup and carburetor. The other between the bike and cup. The bolt gasket helps hold the cup tighter because it allows the bolt to push harder against the cup.
    – vini_i
    Commented Mar 27, 2016 at 14:53
  • 1
    Replace both of them and try again. The gaskets may have shrunk or are dry rotted.
    – vini_i
    Commented Mar 27, 2016 at 16:17

1 Answer 1


Once you fix the carburetor leak, try to start it. Common problems are:

  • air filter dirty- remove the air filter element and replace it or clean it thoroughly.
  • carburetor jets plugged- you said you "cleaned" the carb, but did you completely disassemble and make sure the jets were free of gummy varnish and residue?
  • old fuel- you state that fuel is "1-6 months old", 6 months is too old. You should drain all the fuel and replace with fresh.

Gasoline in most areas now contains a percentage of ethanol (ethyl alcohol) which is bad for older fuel lines and other components. You do not say how old your mower is, but you should inspect and replace any fuel lines that feel soft or gummy. Also, drain and clean your fuel tank and lines, flush with fresh fuel. Ethanol tends to absorb water from the air which will settle at the bottom of your fuel tank over time. You should try to use only fresh fuel (no older than 3 months) in your mower.

  • i didn't know a dirty air filter would prevent starting. i'll change the fuel or add one of those stabilizers. is there a way to check if the spark plug is igniting?
    – Jon
    Commented Mar 28, 2016 at 5:14

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