Packard Forum Index » Pre-War (1899-1942)

In my experience and opinion vapor lock is blamed for many problems where it is not the culprit. As with the subject vehicle other things need to be explored.

As I understand it:

Cold start and run are fine
Problem occurs after the car is warm and it is shut down, then it does not start until is sits fro 1/2 hour.

Here is what I have found:

1. Cold start the choke is closed letting the engine suck in gas to start

2. After a hot run it is shut down and the choke is wide open, thus cannot suck in gas.

3. Problem is often an inoperative accelerator pump circuit which squirts gas in the carb throats.

4. Cooling down for 1/2 hour closes the choke somewhat or 100% and presto the car starts "proving" it was vapor lock.

5. When cold open the choke plate and look into the carb, pump the gas and see if the squirter is working in both barrels. If not, you've probably found the problem.

6. When hot, repeat above.

All of this is great, but it's not isolating a system or a cylinder.

If there is fuel starvation then a few pumps of gasoline from a squirt oil should cause the motor to kick over.

If there is an ignition problem then an adjustable spark tester from NAPA should indicate that as would a plug reading. If the plugs are black velvet colored then ignition is probably weak. As well, I always made sure the timing was correct. Sometimes that meant expending effort to get good timing marks for use with a light. If the motor is turning over fast while cranking the connections are probably good.

Sometimes when those motors are old they are not producing enough compression and cranking the motor for an extended period causes the cold fuel to create enough seal to get the motor going. I had a high mileage Plymouth like that. It had good carburetion and electronic ignition, but when it was hot it had to crank and crank with the throttle wide open to start. So I would check compression when hot, and try a couple of squirts of Marvel oil into the cylinders when hot. If the motor kicks over then it is losing compression.

Thanks, everyone, for the input.
Have not been able to follow up on each idea today...
I needed to take our Third Series Six engine to a shop to be rebuilt.
Will get back to the Super Eight tomorrow...

Thanks again.

Tom,

You are correct that it does no isolate a particular cylinder but just one cylinder is usually not the cause of hard hot starting.

My suggestion does isolate a single system, the accelerator pump circuit. There are many possible causes but only the accel pump circuit can be diagnosed without any tools or meters except possibly a screwdriver (or coin) to loosen the air cleaner.

I find it best to do the simplest analysis first if it is a likely cause. The second simplest would be to compare the cold and hot starting voltage at the starter to diagnose resistance and battery condition.

System or cylinder is standard jargon. Systems like fuel and ignition are inputs. Cylinders are mechanical and generate output. If engineering is blowing up motors on a dyno they might say it has a cylinder problem. Is the problem internal or external, is it systems or cylinders? Is it an input problem or a mechanical problem?

I get called occasionally to handle problem cases of merchandise that can't be shipped because it doesn't run. I'll tell them I have to determine if is it a system or a cylinder. If the thing is cranking over at 900 rpm I'll tell them I have to look at a cylinder because the thing doesn't sound like it has any compression. Most of them aren't that easy. Most of them have system problems and the entire vehicle is totally dead.