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Spent 4 hours chasing a ghost in a Cessna 172 fuel system yesterday

Had a 172 come in with a rough running engine, pilot said it was missing at full throttle. I checked spark plugs, mag timing, even pulled the carb. Nothing obvious. Turned out to be a tiny piece of debris in the fuel strainer bowl, barely bigger than a grain of sand. It was floating around and only blocked flow under high fuel demand. Cleaned it out, test ran it, and it purred like a kitten. My lead mechanic said I should have checked the strainer first, but I learned my lesson. Anyone else ever get fooled by a simple clog like that?
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3 Comments
julia_carter61
My lead mechanic said I should have checked the strainer first" - that sentence right there is the whole lesson. I've been there too, tore half a carb apart on an old O-200 once only to find a fleck of rust in the same spot. It's embarrassing how often the simplest thing trips you up. Now I always pop that drain plug and look at the bowl before I do anything else on a rough runner.
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gracethomas
Wait, a fleck of rust was the whole problem? That's wild. Something that tiny can make a whole engine run rough for weeks. Guess that's why the good mechanics always start with the cheap and easy stuff first.
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abby_morgan18
Honestly, is a grain of sand really that tiny if it messes with fuel flow?
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