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I'm looking for maybe some insight from those of you that have had this problem and corrected it.

My '47 Super Clipper Limo has an issue where when it's been operated for an extended period of time and I shut it off, it's impossible to get it started again unless I pop the hood and let it cool for about 45 minutes.

It does have an electric fuel pump installed (by previous owner) but it's up front, mounted to the frame near the original fuel pump. The pump is wired to run all the time as long as the key is in the "on" position.

I can feel that the pump is creating pressure by feeling the fuel hose between the electric and mechanical fuel pump.

The operating temp is usually below the half way mark. Checking it with a laser temp sensor, it shows that the engine block pretty much stays under 200 degrees while running. This is even while it sits idling for 20 or so minutes and it's in the 80s (temp wise). So I'd say that overheating isn't an issue.

I'm thinking it's vapor lock. But could it be even with an electric fuel pump running? Would relocating it to the rear, near the gas tank remedy this issue at all? What about rebuilding the mechanical pump?

Also, on two occasions, the car quit on me while driving at slow speeds. I had to stop and let it cool down 45 minutes before it started up again after some cranking with the pedal floored. Another time, I was in third and felt the car die. I floored it with the car still in 3rd gear and after a few jerks, it started back up and ran fine.

Any ideas from the experts here?

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Had a similar issue with my 48. I found my problem to be improperly adjusted anti-percolation valves located in the carburetor. The fuel would percolate and empty the carburetor bowl into the intake manifold flooding the engine.

I don't have an answer, but once you solve the problem, I suggest installng an on/off toggle switch to the electric fuel pump, and only turning it on when needed (cold starts, and during vapor lock). I have mine mounted a little further back, but still up front. One usually is told to put it near the back, because it pushes gas better than sucks it. If it's on all the time, that would probably make more sense.

REmove the hood from the car as a temproary diagnositcs procedure. If that corrects the problem then most likely it is gas boiling in the carb. See footnote at bottom of this post about 'vapor lock demystified".

Don't overlook the possibility that your problem may be due to something other than fuel problems. Problematic hot starting can also be a symptom of impending ignition condensor or ignition coil failure.

I was having this issue with my 1951 Packard when after driving around for a while and went to the store. I went back out and it wouldn't start back up so I had to do the same thing just let it sit then after some coaxing then it started back up.
I ended up doing a check on the battery cables and found that the resistance on the wires were much too high. I changed them out and haven't had the problem since. It would be worth a check, the engine even cranks over much quicker than before.

Andrew, I notice from the photo you posted that your engine is missing the fuel pump heat shield. I recommend you get one installed. I believe the practice of installing electric fuel pumps close to the tank is to have the fuel line pressurized, thereby helping to mitigate the effects of vapor locking. I agree with the suggestion to install an On-Off switch for the electric pump. After you correct these items and you are still having vapor lock problems, you might consider adding a gallon of diesel fuel to a tank of gas. You say the Super grade you buy does not contain ethanol? Which brand do you use? Good luck, vapor lock is a nasty thing to deal with and takes away the pleasure of driving our wonderful Packards.

What does the adding of diesel fuel to the gas do?? Is it good on an on going basis? Would a 51, and 53 Packard benefit from this as some kind of prophylactic use even though there aren't any starting issue? Inquiring minds would like to know....

Andrew wrote:

Quote:
Most of my hands-on work on Packards has been with V8s, but this description fits "fuel percolation".

Vapor lock occurs when liquid fuel in the lines turns to gaseous vapor. Diaphragm-type pumps work because liquids aren't compressible, but vaporized fuel IS. As a result, the engine is starved for fuel.

However, percolation occurs in the carburetor. The hot fuel literally begins to boil - foaming up through the bowl vents and down into the carb throat. The engine then acts like it is loading up or flooded.

All this is really nothing new, but modern fuels contain higher levels of alcohol and have made things a bit worse for our old carbureted vehicles.

The factory installed fuel pumps shield for a good reason; too often, the less-informed discard them in the course of routine service.

With everything else in proper working order, another trick is to "insulate" the carb from the heat of the manifold. Some manufacturers used two or more gaskets. I've recommended a a thin piece of phenolic board, trimmed same as the base gasket and then sandwiched between two if those gaskets. Those who have followed this often report success.

As this appears to be a common problem, I've held back some general info in favor of a FAQ post that I'll be working on.

"Had a similar issue with my 48. I found my problem to be improperly adjusted anti-percolation valves located in the carburetor. The fuel would percolate and empty the carburetor bowl into the intake manifold flooding the engine." - Telephone Man

Besides ordering the heat shield for the fuel pump, I'd like to properly adjust my anti-percolation valves as well. How do I properly undertake this project? Can you refer me to any reference material?

Thanks for all the great quick responses.

I would have to say that after hearing many of the responses from the collection of wisdom here, that my issue is very likely the fuel foaming issue and not vapor lock. In order to get my car started I have to treat it like it's flooded by pushing the pedal to the floor while cranking the engine. Once it starts, I get a lot of white smoke for a bit and some, what I think, is unburned fuel out the tail pipe while I have my foot on the gas in order to keep the rpms up until the engine smooths out after about 10 seconds.

As far as the heat shield, thanks guys, I didn't even know there was one missing. I'm going to order one from John Ulrich.

The other thing is that I'm going to drop the gas tank and have it cleaned and coated this winter. I figured I'd do that because I have to replace my sending unit as my gauge is bouncing around quite a bit. Not sure if it'll help with the fuel delivery issue but in any case, it can't hurt.