Hello, my '74 Buick Wagon has a rebuilt carb. Recently replaced fuel sending unit and drove fine. Now- three months later the engine won't run more than a few seconds after starting. Wondering if sediment from tank filled the filter? Where is the filter? Thanks!!
There would have been a filter at the end of the pick-up tube on the sending unit, and presumably that was replaced when the sending unit was replaced. The other filter is in the line between the fuel pump and carburetor, right at the point where the line connects to the carburetor. This assumes you have the original Rochester carburetor. I don't know that it's exactly the same for your car, but on both the '67 and '78 Oldsmobiles I own, the fuel filter is located where it's circled in yellow in the photo below. To get it out, you first want to unscrew the line where it attaches to the fitting. You want to use a flare wrench for that so you don't round the nut. You'll also want to put a wrench on the larger end of the fitting to hold it from turning. Then remove the fitting itself, and the filter is inside. Make sure the new one is installed in the correct orientation, with the open end facing away from the carburetor. Also make sure that you put the spring back in, or the filter won't be held tightly in place, and make sure you replace (reuse the old one, or put in a new one, which the new filter will probably come with) the o-ring seal, or you'll have a constant drip of fuel no matter how much you tighten the fitting.
By the way, I had a similar problem with my '67 Delta after I had removed, cleaned, and replaced the fuel tank and put in a new sending unit. Even though I had also replaced the fuel filter, it wasn't long before the engine began to stumble significantly at highway speeds and even at lesser speeds (30 to 40 mph). It would start and idle ok, but I could never get up to speed without stumbling and hesitation. I took out the new fuel filter, which by now had several dozen miles on it, and it was pretty dirty. I assumed that my fiddling with the fuel system had stirred up some long-dormant crud, which had gotten trapped in the filter. Replacing the filter cured the problem, and it has run fine ever since.
As jaunty75 says, the filter is in the carb body presuming stock quadrajet. One thing to also consider is when you replaced the sending unit that the rubber hoses weren't fully tightened or are leaking. If they can't get a good connection on the tank it will pull air instead (easy test is to fill the float on the carb so it can run off of that for half a minute or so). There's all sorts of other possibilities too, from junk in the carb to a sticky float, but the easy ones are the first to try.
About those hoses, it's not sufficient to just tighten them once. They seat in which requires tightening the clamps at least one more time. If I remember correctly, the Quadrajets originally had bronze filters of which can get cleaned and re-used. You might end up removing and re-installing the filter several times, depending on how much mud you've stirred up. What I would do, just to be on the safe side, would be to remove the fuel line placed between the pump and the carburetor and then set it aside, for restorative purposes. Then, get or fabricate a temporary cut-in-half line, for installing a good old transparent filter. That way, you'll always know when to dump out all of the mud and moisture. I'd be wary of where the filter is to be located, though. You don't want it near any heat source resulting in vapor lock. Once you're confident that the system is finally cleansed, you could substitute the fabricated line with the original
How many seconds is a few? If it craps out right away after releasing the key look to the resistance wire to the coil + terminal. If fuel starvation is suspected try stroking the throttle after the engine has died and watch for streams of fuel into the throttle bores. If none then you have a fuel delivery issue. As already mentioned the filter is in the fuel inlet, the big nut which you need to be very careful not to strip since it requires a large wrench and the threads are fine, the metal soft. If this was sudden onset you might also want to start examining all those vacuum hoses. A big vacuum leak can cause stalling, especially when cold.