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My son and I have a '65 Malibu with a ZZ4 350 crate motor and an Edelbrock Performer 1405 600-cfm carburetor. We never had any starting problems until we had the trunk floor and gas tank replaced. Now, if the car sits more than two days, it loses prime and will not start unless I pour a little gas in the carb. If it is driven every day, it starts fine. I thought it might be the fuel pump, so I replaced it with a new stock mechanical one. The car runs great if started within two days. I pinched the fuel hose 2 inches from the carb and let the car sit for a week, and it started right up after releasing the clamp. I can't see any signs of a leak but have not had the car on a lift to get a better visual. Any ideas where to look? Everyone has a different idea, and this is making me look bad in front of the boy. Help!
My research indicates that many people complain of similar scenarios with the Edelbrock carburetor. Why you didn't have the issue before is quite perplexing and is still to be determined, but I've discovered myriad discussions regarding your symptoms. Percolation and evaporation seem to be the main hits, and a lot of the reasoning seems logical, although I don't really see percolation being applicable, given the parameters you've laid out.
As my father always told me, you go back to what you changed last. In this situation, that would be the gas tank removal and replacement. However, that's somewhat hard to believe this time around, as one would think you'd see an obvious leak if the problem were related to said replacement. If the fuel line had somehow gotten a small crack in the process, that could potentially help the system introduce air, drain back, and “seek its own level” more easily, but clamping the line 2 inches from the carb to “fix” the problem doesn't add up with that. Confusion sets in.
I called my friend Philip Vickous at Quick Fuel Technologies for some input. Mr. Phil knows his business and, like me, is a logical sort of guy who relates A to B. We both want to tie it to the gas tank replacement, and where I considered a compromised fuel line, Phil thinks it could be a venting issue. Had you not mentioned the tank replacement, but did offer up the clamping fix, Phil felt as though the culprit may be the pump (and associated valving) creating a suction (new pump be damned). If the tank is not vented properly, the system can be pressurized, and as it depressurizes, it sucks fuel back into the tank. I really didn't think fuel could be pulled back out of the carb, but Phil says otherwise, under the right conditions. So first up in the diagnostic path is to get the car in a normally running fashion, remove the gas cap, shut it down, and come back in a time frame that would generally produce a no-start condition. If this addresses your issue, Mr. Phil is the man, and you know where to go.
If this doesn't fix the problem (and I was in your shoes), my simple little pea brain would do the following sorts of things. First off, even though I'm sure it probably doesn't have a damn thing to do with the problem, I'd rebuild the carburetor. I'd also add a phenolic spacer and wrap the fuel line from the pump to the carb in an effort to insulate it. Again, it might not do anything, but it's worth a shot.
After I most likely wasted my time and effort with that, I'd get the car back in a normally running fashion, shut it down, and once again return in a time frame that would generally produce a no-start condition. I would then first determine which way the fuel went, in or out. Does the oil stink? Is the intake plenum soaked? Are the plugs wet? Does it reek of gas? If not, then it probably didn't go in the motor; it either evaporated or went backward. I'd then start checking for where I had fuel. Check the float bowl first and start heading down the line, literally. Keep in mind that the float bowl might be empty, but the accelerator pump can still have fuel in it, so don't let a squirt or two fool you. If it's simple enough, install a clear filter in line between the pump and carb to aid in the process.
If you don't find anything along the way that jumps up and says “pick me,” an electric fuel pump will certainly take care of things, but if it really never did it before, well then obviously that shouldn't be necessary. Here is a link to a very inexpensive street unit offered by Summit Racing: summitracing.com/parts/edl-1791/overview. Lastly, my simple Vulcan logic dictates that if clamping the line 2 inches from the carburetor with vice grips consistently remediates the issue to a satisfactory conclusion, then an in-line shutoff valve would have to accomplish the same result and be substantially cleaner and significantly more user friendly.