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Twice now after cruising in warm weather (85+)for about 45 minutes, then stopping and re-starting in about 5 minutes, my '74 starts to buck, then eventually stalls. Only after waiting 10 minutes or so, can I get it started. I have a mildly-built 351C with Holley 650, double-pumper, mechanical secondaries, on an Edelbrock 4V Performer. I have a 1/2" phenolic spacer (HAD a 1" aluminum). Sounds like vapor lock. A similar thing happens when I accelerate hard, then completely let off the gas and brake hard. Nothing more embarassing than stalling at a red light! Any words of wisdom?

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...Which side of the Fuel Pump is the Filter mounted in the fuel hose? It should be in-line on the 'Pressurised Side' between the pump and the carburator. IF it is on the Vacumn side (between fuel tank and the pump), when HOT the fuel May 'Boil' inside of the filter, especially if it is of the 'tin can' type. When this happens your fuel pump will be 'trying' to pump Vapor; hense the term 'Vapor Lock'. If this is not your case; you may have a clogged filter in the carb inlet (Holley). OR/AND the fuel lines around the pump may be getting over-heated from being to close to the header primaries, a thermal covering may help here. While we are on the subject of 'fuel starvation'! Here is a word of warning about something not many people realize; I am speaking of the HOLLEY fuel pressure REGULATER (that 'neat' little Blue painted aluminum thing, that is adjustable). If you have ever taken one apart, as I have; you can't help but notice that ALL the fuel that passes through this device MUST go through an Orifice with a Very small Diameter of aprox. .150" (I'am guesstimating here because I did not actually measure the 'Ball Seat',but it is that tiny. My point is that at top end high revs, fuel starvation would be expected! And when I use to run dual quads (on another vehicle) I, at least, used one regulater for each carburetor. BUT that is still, ONE small Orifice to 'Feed' 2 FloatBowls. Good-Luck with it!

If you have an in-line filter between the pump & carb, I suggest pulling the sintered filters & leaving them out. Double filtration is uneccessary. They should not be contaminated by the way, the in-line filter should have prevented any contaminants ever reaching the sintered filters.

By the way, what rpm do you have your idle set at?

...Yes Kaamakat!! Good Idea, it very well could be the gas cap is not vented...And SwenDog I have to tell Persons that run those 'GLASS Fuel Filters' That they are Dangerous! If you look at the threads where the sections unscrew, you can see that the threads are flat and shaped more like 'Teeth'. The metal is a weak kind of 'peuter', these teeth break-off and the ends come undone resulting in spilled Gasoline all over the place. And when Pressurised it sprays a mist all over. It happened to me, in the past, when I just barely tightened the ends up. I advise You to get rid of it and go to a metal can type, and NO plastic filters. Being able to 'See' the dirt, and fuel flow, in a Glass filter is not as important as NOT seeing Your Pantera go up in Flames. Besides that; they are Not allowed onto most Racetracks. Just friendly advice, from experience.
Check your fuel level in the fuel bowls while you are at it. It could be too low, staving for fuel or too high. The stalling at a hard stop almost sounds like either the rear bowl is set too high and the excess fuel gets dumped into the carb via the vent tubes or the front is too low and the jets become starved for fuel on a hard stop. Either way check the fuel level, try pruchasing the aftermarket clear windows that they sell for future fast checks. Fuel should just leak out of the bottom of the window, I think 1/32" below the threads is optimal.

If that seems to be OK...check the float fuel meter (cannot remember the right term for the fuel flow valve). This is that flat hex nut on the top of the bowl, remove the jam nut and unscrew the valve. It might be clogged or have some material in it preventing the valve from opening or closing when needed. Lastly you can check the carb floats to make sure they are not getting stuck and binding.
Thanks for the added feedback. As with many things, this is the way the car "came", which as we find out in time was not "correct" (re: the glass filter). First order of business is to pull that and replace. There's a Fram HPG1 cannister type that Summit sells for $41.95. Would this be a good choice? While I have the fuel lines off, I'll remove the inlet filters for the carb and install the see-thru float sights. As far as the venting is concerned, I have a non-vented cap. Is a "vented" replacement easily attainable or is this another weirdo-Italian size? I would THINK that the tank would HAVE to be vented if the gas cap were not.

Nils, Usually stalling after hard braking is due to the floats being set too high. This can be tricky on Panteras due to the engine sitting level instead of tilted as in a conventional layout.
The manifold tilts our carburetors high in the front so I would consider adjusting the front bowl a little shallow and check for stall at braking.
Make little adjustments, 1/8 turn of the float nut and then test drive.
There is a vent hose coming off the top of the fuel tank on my '73 L. It can be viewed under the little black wing that also supports the engine screen. The vent has a tube on it running down in front of the tank. So, if you have such a vent on your Pantera gas tank, there should be no need for a ventilated gas cap.

When my Pantera was vapor locking, the phenolic gasket between the carb and manifold did the trick and stopped the vapor lock.

Now might be a good time to inspect the fuel pump, taking a systematic approach. If it's a mechanical fuel pump, some of them can be disassembled. Inside the mechanical fuel pump, there's a rubber diaphram to pulse back and forth, pumping the gas. It should be free of cracks, be pliable and have a good seal. I have an electric fuel pump, and I went ahead and just replaced it anyway, so as to eliminate that as any source of reliabilty issue in the near future.

Modern vehicles, with fuel injection, usually have two fuel pumps, one in the tank (primary pump) and one in-line, en route to the injections system (secondary fuel pump). When a car runs out of gas, the primary, in-the-tank fuel pump will over heat and cause the same symptoms you describe. That's why I mention the fuel pump as an item to attend to.
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