Sometimes after I turn the car off it doesnt shut off right away. It putts and sputters just BARELY turning over and it does this for about 3 sec after I turn the key to off position. What is going on?
(I have a Chevy 350 with a 650 Holley Carb)

 

i believe its called "dieseling", use better gas and it should go away, your carb may be really rich too.

its not good for the engine, so if it does it, turn the key back on and the car will go back to running, then put the car in gear or nuetral and then it will shut right off.

 

thanks

 

Also check for vacum leaks.

 

Typical causes:

Vacuum leaks
Idle set too high (often as a result of poor tuning, needing high idle so as not to die idling in gear)
Timing too advanced
Crappy gas
Too much compression
Spark plug heat range too hot
Oil on the plugs

Since you have a Holley, cause #2 is pretty likely, if you haven't leaned the jets and bumped the power valve up several sizes and otherwise dialed it in.

 

also run something through the engine to clean it out, it can be caused by carbon buildup in the cylinders. try pouring water or atf into the carb (with the engine running and one hand on the throttle) and keep it goin until the smoke stops comin out the exhaust and it idles without trying to die.

edit: tho it might be better to get some sorta fuel additive cleaner, i've ran water through mine with no ill effects and the atf is entirely hearsay, albiet from a reliable source

 

why does that NOT sound like a good idea to me?

 

never pour water in anything in a car. get some Seafoam and pour it straight into the gas tank, or carb (carb for quicker cleaning) also toss some of it into the oil. it has it on the bottle. get it from any auto parts store

 

what problems could occur when pouring clean (distilled) water through your carbureted engine, when it's running and warmed up, other than the possibility of pouring too fast, hydraulic locking the engine? this used to be a popular method of decarbonizing your engine before the fuel additive cleaners were around. as for using ATF, i was told about it by two different people, both aircraft maintenance engineers, one of whom had 30+ years experience in piston engine maintenance, aircraft and automotive. so i'm just curious, i know at first it does sound like a bad idea, but i can't really think of any reasons why so any input would be appreciated.

in fact, in my mind, adding a non-detergent based cleaner to your engine oil seems a bad idea. unless it's designed for that, i'm not familiar with this Seafoam cleaner. i'm not looking to start any sorta argument here, remember we're all on the same team, just to expand my knowledge of these things so any reasoning behind good/bad practises is most welcome.

 

did a bit of research, apparently both methods are still used today especially in off road and marine engines, atf seems to be more common although from what i read, it can foul the catalytic converter if poured too fast.

 

I use water in my carb'ed motors for cleaning combustion chambers, it works great. I use a spray bottle though, to minimize the chance of pouring too much at one time.

ATF also works great. I usually use it in the spark plug holes for motors that have been sitting for a long time or that haven't had oil in them.

 

I've seen spray bottles of water used with great effectiveness