After I rebuilt my motor on my 79 and got everything all hooked up then fired it up, I had a rough idle. It was obviously a fuel issue, so I pulled the carb, found a few issues and rebuilt it. I then restarted the car and it still had a rough idle though it had improved some.
I then turned to the idle stop solenoid which is another common trouble spot. I tested it and cleaned the ports with some spray carb cleaner but it didn't help...still running rough. I found that closing the choke smoothed it out and realized it had to be a sizable vacuum leak. I checked all the vacuum lines (stock 79 emissions) and they were fine. I checked the power brake booster line and it was fine.
I then popped the fuel lines and found fuel pouring out of the fuel return line at the carb even though the car was off. I removed the gas cap and there was significant pressure built up. Looks like I'll need a vapor check valve. I then loosened the gas cap.
I tinkered for a while, started the car several times and couldn't find the issue. Then...the car wouldn't start at all. I checked and had no fuel pressure because the mechanical fuel pump went out. How random is that? I believe the built up pressure in the tank blew out the diaphragm in the pump. So, I swapped it out with another that I had and it fired up but still ran rough (gas cap off so it wouldn't build up pressure again).
I then retreated to the living room for the night and visualized the entire intake system. After some thought, I decided it was most likely a bad gulp valve. Tonight I swapped it with a spare I have and it runs absolutely amazing now.
I think finding the problem made the rebuild all the more fulfilling! Now I can turn my attention to the other things that need to be addressed. She's coming together!
Yeah!!!
