How Could I Be So Stupid/Careless?

I began taking High School Auto Shop as a junior in 1972. Circa 1995, I was re-building a small carburetor belonging to a 1984-84 Dodge Caravan 2.2 liter four-cylinder for a customer of my then mobile auto repair. Every one knows to be very careful about insuring nothing falls inside the intake manifold when removing/replacing/storing the carburetor.

Well, after the rebuild when I went to install the carb, I only found three carb attaching nuts. This really befuddled me because of the caution I always employed when during such repairs. I don't remember if I looked inside the intake manifold for the fastener or not. I must have found or purchased a fourth nut in order to re-install the carb.

Later, I was driving the same vehicle over to get a smog check (California) and the little four-cylinder began to miss and loose power so I aborted the smog appointment and drove back. Lo and behold, I found a cylinder chamber all chewed up (along with the spark plug) where the nut had entered the combustion chamber. Unforgivable error on my part, but at the same time still unbelievable it could occure with someone so careful as myself. I had to rebuild the cylinder head.

If you like, be sure to include below any mishaps you have experienced (your own fault) that should have/could have been avoided. Thank you.

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I did something very similar involving an air cleaner wing nut when I was......17 I think. It was my sister's 76 Chevy Monza 2+2 hatchback with the smallest ever 262 (4.3L) V8. Since it was my fault, Daddy made me fix it out of my own pocket.......so it got what I wanted to put in it. A 1971 low mileage small block 400. That car would obliterate the rear tires at will for as long as you held your foot in it. It also introduced me to how quick Monzas could be. I had four myself after that. lol