Okay, I'll be the contrary SOB here.
How do you know this? Have you seen or heard boiling fuel? Have you measured the pressure? Do you know the boiling point of gasoline? Have you measured its temperature?
Did it really help, or did it just seem to because you put a bunch or time and money into it?
This is the normal condition. An inline fuel filter will not fill up. It will contain air.
Again, this is completely normal. You are fixing something that it not a problem.
This is why the best choice is a metal filter: You can't see the air inside and get upset.
That and the whole "Not breaking and spraying fuel all over your engine" thing.
Do you have a factory service manual for your car? If not, you need to get one. It will show all of the lines and connections that the factory put there, which will include evaporative emissions equipment that is no longer there. From there, you can figure out which lines go where and connect them as appropriate for your needs.
Factory service manual.
My recommendations, in no particular order:
- As others have said, there are a lot of variations on gas caps through the '70s. Only one type will fit. Whichever type that is is the one you need.
- The original system vented the tank in a complex way. It's gone now. You need to have the tank vented somehow, in a safe manner, as 67Dart273 described above.
- All cars benefit from a return-circulating fuel pump system. As far as I know, yours had one when it was made (others, please tell me if I'm wrong). The correct mechanical fuel pump, with a recirculation nipple, connected to the original recirculation line, connected to the original recirculation nipple on the sender, will do the job, and you won't need a mechanical fuel pump, or a fancy fuel filter.
And now for my actual point:
You have "stumbling" after stopping and turning off the engine while warm.
You have decided (without evidence) that the problem is "boiling" fuel, and have taken a number of steps to fix that, and they haven't helped.
Your problem may be fuel that is boiling so tenaciously (but only while stopped) that it is resisting your efforts, or you may have a different problem.
An electrical fuel pump, "pushing" from the tank, will solve darned near any vapor-lock or "boiling fuel" problem. If, in fact, you have no liquid fuel whatsoever in your fuel lines or your float bowl, whether you have fuel vapor or air, the electrical pump will push fuel through and fill the float bowl in a second or two. In this case, all you would need to do would be to turn on the key, wait a second or two for the sound of the pump to change, indicating that it has built up pressure, and start the car, and it would drive normally.
Also, an electrical fuel pump, not connected through the oil pressure sensor or some similar means of automatic disconnect, will continue to pump out your whole tank in the event of a crash, just so you know. I've hooked them up without a safety, we've all done it, but you've only been doing this for a month, so it bears mentioning.
If you would describe your problem in more detail, that would help us to help you.
"Stumbling" is not very descriptive.
Personally, I suspect that your carburetor is "loading up" (ie: a "too much fuel" problem), and that you need to start it with the pedal floored and "blow it out" before proceeding.
This should not represent "normal operation," but is how one deals with this problem in the short term.
Have you rebuilt your carburetor? Set the float level? Is the float sinking? Is the needle and seat leaking?
These are all of the questions I would ask.
My final recommendation:
Go get a "Zip Kit" for your carburetor, as well as a float and a gallon or two of evil carburetor-soak cleaner, take the carb off, read the factory manual, take it apart, clean it, rebuild it (you'll also need a source of compressed air to blow it out while cleaning it), reinstall it, adjust it, and see how it works.
Good luck!
– Eric