'77 another fuel delivery problem

[Rupesy]

I did see another post but this is a little different. A few weeks ago, RustyBelle stalled out close to home. my daughter pushed her down the street to the house. I was out of town and got home a day or two later. I pulled the top off the carb, looked around, checked the needle and seat. Everything looked fine, but decided to rotate the needle. Put it back on, sprayed some starter fluid in and got her running just fine, went and filled up the tank. Didn't happen for a few more days and she had some random issues but she always made it where she was going. She did die just as she pulled into an event she was attending, however, she started up just fine a few hours later. On a hunch, I decided to put a new needle and seat in and seemed OK. Got a call from my daughter stalled out down the street from home to days later. Pushed her home again. Pulled the top of the carb and everything appeared to be fine, but float bowl was empty again and could not get gas to flow after reassembly. This time could not get her started. Now I am really curious. Standing there stumped, a lightbulb turned on and I thought what if I unscrewed the gas cap?? Well, it worked! After a couple of cranks she fire up. So now I am trying to figure out why there is enough vacuum in the tank to keep the fuel pump from pumping (pump is only about 6 months old). Any ideas? I do not have a check valve on the return line, but never have had it. Carb is recently rebuilt and has been working great for months. Seems like the vacuum must dissipates after a few hours, but then generally builds after a long drive.

[TimpanogosSlim]

What condition is the evap (charcoal canister) system in?

[Rupesy]

That's a good question. I have never messed with it. What would you recommend?

[btoran]

the fuel pump is relatively new, but is it good enough and installed properly? i had a problem with mine that rotating the pump helped fix.

[TimpanogosSlim]

Was just thinking - if indeed you are able to pull a vacuum in the gas tank, which is maybe doubtful, that shouldn't be possible unless the check valves in the evap system are clogged. And I'm assuming there are check valves, I guess.

[toplessexpat]

Or is the return line to the tank partially clogged?

[TimpanogosSlim]

sounds like a job for an air compressor. take off the cap and see if you can make bubbles from the hard lines under the hood

[Rupesy]

It doesn't seem possible to have a vacuum condition to me either, but since I loosened the gas cap, not a single problem all week. Could be a symptom of something else.

I will blow some air through the return lines and see what happens. Where are those check valves located?

[TimpanogosSlim]

I think the check valves are in the trunk but i don't know for sure.

If i get a chance, I'll look in my "Factory" manual and see. i have a 77 as well - mine is late 77 with the alternator on the cold side.

[AriK]

There's a one way check valve in the vapour line near the charcoal canister. There's a two way valve underneath the car over the rear axle before entering the trunk. There's also a 3 in 1 separator in the trunk, driver's side fender.