So the fear that in a closed system, that a carb bowl would be because if it wasn't the engine would run right because it would be sucking in air instead of gas...
Ummmmm... closed system?? If it's a closed system, how is it possible for gas to run all over the ground when the float sticks with the needle open??
Small engine carburetor float bowls are vented... if they weren't, they wouldn't gravity feed.
The carb sucks the fuel from the float bowl, not from the fuel tank (which is also vented or it couldn't gravity feed).
Float bowl vents are configured differently depending on vintage, model, and whatnot... many older type vent directly to atmosphere, many newer use some sort of internal vent that may even lead to the crankcase (which, depending on conditions, may be quite rich in moisture). Some use a check valve or ball to reduce inverse venting... which will reduce incoming moisture (if it's working... questionable if it's sat with E10 fuel in it).
Believe me, the air in a float bowl, and more so in the fuel tank, is exchanged more often than you think... especially on older stuff.
The fuel in the float bowl is quite often the first to "sour". In years past it was common for a float bowl to have a manual drain on it... if the equipment had sat for any length of time you automatically opened the drain to let the old fuel (and any water if present) run out and fresh fuel run in before even attempting to start it. You don't see those drains anymore (not as often anyway)... the EPA don't like them. I needed a new float bowl for a little snow thrower with a Tecumseh 2-stroke last fall... the old one had a spring loaded drain, the replacement did not. The owner (neighbor) used E10 in it the year before, the phase separated E10 ate a hole right through the bowl (which was a good thing... all the E10 from the plastic tank ran out on the ground where no further carb damage could be done).
LOL - My neighbor is a big ethanol supporter, but he's beginning to see the light. Last spring he got to replace his Poulan leaf blower (I couldn't save the carb), last fall was the snow thrower, and this spring his Briggs generator started, ran rough for a few seconds, died and won't restart (ain't looked at it yet... but, I've got a good guess
).
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