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Instead of armchair theorizing I almost always rely on my actual experiences of the past 56 years. I've had the above problem on numerous cars, the latest on our 25,000 mile 52 Patrician factory show car.

I drove out to the 2015 national meet in Reading PA on a hot hot summer day, it ran perfectly and it drove perfectly on its 4 original tires. So much for "replace them after 5 years!"On the return trip, again on a hot day, it stalled when coming to a stop from 50 mph and would not restart.

On analysis the accel pump was not working and it was caused by the external accel pump linkage becoming disconnected because the clip fell off. Cranking it with my hand over the carb made it start immediately.

So much for "vapor lock" again.

TO SHINYHUBCAP:

Our parts business has nothing to do with my correct or in correct mechanical advice, there is no need to apologize except....your choice of characterizing your comments as "picking on" is quite revealing.

I'm fully able and at ease with admitting a mistake and correcting it when I'm in error. I would hope that in the interest of fellow Packard owners that they will do the same.

car wont start without "priming" cont:

Lets review the changes in chemistry of gasoline down thru the years to get a better understanding of why some cars wont start when they are hot.

If we go back to the early twenties, we will see your Packard had something called a "Fuelizer". It was nothing more than a spark plug in the intake manifold !

The fuel of that day had such a high boiling point, best way to get your car started on a cold morning was to start "lighting the fire" in the intake manifold.

How to make it easier to get cars started on a cold morning? Increase the Reid Vapor Pressure - i.e. make the fuel more volital.

The introduction of devices like the vacuum tank of the 1920's, and the "suction type" fuel pump in the early 1930's standardized fuel supply from the tank to the motor (with the exception of the Ford Model "A", which had the fuel tank above the engine, right behind the dashboard..!

The introduction of "suction style" fuel supply ( again...either the vaccum tanks of the 1920,s or the "suction style" fuel pumps that came out in '32, caused additional problems.

Because when you suck fuel along the underside of the car, where heat from the engine can warm the fuel lines, you help the fuel boil over.

"suction style" fuel pumps cannot pump vapor; you can wrap all the clothes-pins and cow magnets around the portion of the fuel line that you can see - the "pressure" side from the pump to the carb. - but that wont change what happened in the "suction" side of the gas line between the tank and the fuel pump.

Fuel and car engineers correctly recognized if they lowered the boiling point of gasoline, cars would be easier to start during the cold winters of the north-east.

As the "Reid Vapor Pressure" went up, Packard Service Bulletins by the early 1930's were full of articles trying to resolve the vapor lock problem.

The symptoms described by the fellow who started this "thread" suggest it is a simple problem of using modern fuels in a pre-fuel injection vehicle. Which explains why a electric fuel pump (which pressurizes the fuel line, thus preventing vapor lock) is the simple and permanent solution.

I have no real idea - only some suspcions, as to why some of the later pre-war "junior" Packards and most of the post-war ones - again - SOME, do not seem to be afflicted with the "vapor-lock" disease. Could it be that Packard engineers figured out a way to keep the fuel lines cooler than the earlier models ?

As a side note - don't make the mistake of thinking "we all use the same gasoline". Nonsense ! Depending on the season you are in, and/or the region you are in, the Reid Vapor Pressure of gasoline is changed by the refineries, to best meet the needs of the average driver in that area. Well...that WAS the case during the carb. era - I don't know if they still bother to do that now that you cannot buy a new car with a carb - all have high pressure fuel pumps located IN the gas tank.

Gee, all this arguing and the poor guy just wants some help.

The priming test idea is excellent. And nobody has told him that.

So what I would do is get the car good and hot, drive it home, shut it off for an hour, and take the top off the carburetor. One of my old GM carburetor books says that a partial vacuum caused by a fully closed throttle can empty a carburetor. But if that motor doesn't have an anti-flood drain that idea is blown up.

I would do a compression test on the engine. It could be that the engine doesn't have enough compression to pull gas and the priming creates enough of a seal to get it started. I

I just had this kind of experience with my 19 year old modern car. I pulled off the freeway for gas, filled it, and when I pulled out it lost power and wouldn't go over 25 mph. First I called the station just to check - their tanks are new which is why I go there. Next I checked ignition and fuel - both good. So I pulled out my compression tester and found two low cylinders. Yet the car idled perfectly. After adding oil the compression came way up so I knew the engine was gone. Just like that the rings stuck. I threw some Risolone in it and drove it to the dealer. That engine was weak for years and I knew it because I did compression tests. I don't have time to fix it so I bought a new car.

My car sat for 7 1/2 years with gas in the tank. I siphoned some out and it is not lacquer. I still don't want it going thru my system. What is the best way to empty the tank? Siphon it all out seems easiest. Then where do I take it to dispose of it legally?? NAd the fuel lines, are they full of the old gas too? And carb. It leaked when the mechanic started it for the first time. There is a small hole in the carb where it look to me like a screw should go but no threads. A guy said maybe a small nipple goes there from Auto Zone. Any information is helpful. Will the carb always leak or perhaps stop once it warms up. Yes, I will have it rebuilt but can't now.

A picture of the "hole" in question will let us know what you are seeing.

Over the years, things disappear on cars. So things like fuel pump shields, and the insulator block between the manifold and the carb. Both can lead to fuel boiling/percolating.

During carb manufacturing passageways are drilled through the outside of the carb to a spot inside to create an internal passageway for air/gas.....the outside hole in the carb body is sealed with a soft metal plug; I believe it's called a welch(sp) plug. These plugs can leak or fall out. Might this be the hole w/o threads you speak of? Hope this helps.
The fix is pretty easy, if the plug is still there and leaking use some JB weld to seal and afix the plug.....
If the plug is gone I have used JB weld to fill and seal the plug hole. As big Kev stated "a picture would help"
Regards,
Steve

Just a humble suggestion. When the engine is hot, and the starter is old and on its last legs, it will draw a lot of power to turn the engine...and then there is not enough spark (power) to fire the engine.

This condition can be checked by adding an additional battery to the system with a couple of jumper cables...If the engine fires, then it is worth having the starter checked.

As part of the same system, make sure that your battery cables are 00 cables and that all of your connections are clean and tight. Also check to see that your battery is in good condition and not on its last legs.

A little holy water on the hood ornament also helps. Ernie

My 51` has a similar issue. Only it happens when it sits for 2 weeks or longer. The choke plate is down but it cranks forever with me pumping on the pedal like mad. I stopped doing that and just pour some fuel down the carb and bingo good to go.

That is where a rear mounted electric pump pays for itself. My usual procedure is to run the pump for 10 seconds or so to get gas into the carb. Turn the key off and pump the gas once or twice to set the choke and prime. Turn the key back on and hit the starter. Generally it then fires fairly quickly and once the engine is running turn the electric off. Saves all that cranking and possibly overheating the solenoid and starter.

Starters do not like to be energized for more than a few seconds at a time. On the pinion shift solenoids used with senior starters, heating the solenoid coil can be a real issue. Heat can distort and expand the winding form and cause the plunger to stick in the bore. I have one of the senior Autolite solenoids with that very problem. The coil form distorted so the plunger cannot slide in so solenoid is no longer usable..