So my 79 started up and ran very well with no issue, it idled very well and I never worried about it stalling at a stoplight. I recently (last week) changed the airfilter, pcv valve, pcv filter, a leaking rubber fuel hose, fuel filter (I found out when I was changing the filter it had an incorrect really long, bent fuel filter) I then changed the old beat up air cleaner for the correct original one and it seemed to run better. I was driving home last night and the thing stalled on me multiple times, would be hard to start and then die again a couple seconds later. I don't think the hot air pipe and other flap in the air cleaner ever open, would that cause this condition? Also I included a picture of the vacuum hose for the second flap, when I pull that hose out the flaps open letting air in, it is currently connected to a vacuum port on the back side of the carb, is that the correct port? Are those two issues (flaps not opening, and stalling/hard starting when warm) connected?


In this pic you can see the vacuum line coming off the passenger side flap going to the vacuum port on the bottom of the carb towards the back. Is this correct? If it is, what would be preventing the flaps from opening as the car gets warm?

 

Okay, so after doing some reading on this forum I believe the phenomenon I experienced was vapor lock. I had been driving the car periodically that day, and it was warm when I went to drive it home. When I got home and took the air cleaner lid off I did notice smoke/vapor coming out of the carb. I checked today to make sure I had a connected fuel return line (it does) and I didn't notice gas continuing to drip into the carb when the car was off (and warm). The car is 100% factory no modifications, do these cars vapor lock that easily? This weekend I'm changing the thermostat to a lower temperature one (who knows how long the thermostat has been in this car) and flushing the system, would that help with a vapor lock issue by keeping the car cooler? Any tips?

 

I seriously doubt that it is vapor lock. Especially if you have made sure that your fuel return hose is attached at the fuel pump and also back at the fuel sending unit on the fuel tank. On cars that have sat a long time...I have had to remove the fuel door and bezel...remove the fuel return hose at the sending unit(smaller diameter hose of the two coming in from the passenger side)...install a union and attach more hose to the fuel return hose and crank the engine and see if fuel flows back into the tank where I have positioned the hose to allow the fuel to flow back into the tank. I have had them be all connected...but the fuel return steel line was plugged.

When you replaced the fuel filter...was it the one that is located in the front area of your Quadra-jet Carb??? And was it the paper type that has the check valve in it??

You can possibly have an issue with the fuel "S" supply hose at the fuel pump. I have seen them suck shut and cause a car to starve for fuel and or die.

Yes the hose connects to the back of the carb...but there are often two ports. You can remove the hose...cap off that port and drive it knowing the flaps are open and see if anything changes. Hot air tube is not going to effect or change your problem. it is a pre-heater for air going into the carb.

Need more information. Idle RPM's?...is it a smooth idle? Any vacuum leaks...such as leaks from headlight relays. Disconnect hose on the vacuum fitting at the back of the carb on the intake and plug it and test drive it and see if it does it. often times the actuator relays can leaks and cause a problem in a rough/stumbling idle. Timing? assuming the notch on your balancer has not moved giving to a false /inaccurate reading when using a timing light. Vacuum advance working???? With the ported vacuum switches located in the thermostat housing/intake at the front...are they working as designed.

Choke closing when it dies??? Seeing a light vapor coming out of the carb after driving is normal to some extent. But is depends on if it is flooding while driving. If you have not seen excessive fuel pooling on top of the carb or leaking onto the intake..i doubt that you have an "Old FaithfuL" scenario....which is basically a stuck float.

DUB

 

Before you tear too far into this check to see that you installed the filter correctly in the carb. If it's in backwards you'll get some fuel to the carb but it will intermittantly starve for fuel then will start up again then starve again and idle or drive slowly then when you start demanding fuel it starves and dies.

 

As far as the fuel filter I consulted the Haynes manual and it's oriented and installed as directed by the book. The previous fuel filter that was in there was twice as long as the correct one should've been and was crunched in there and the spring in front of the filter was flat/almost flat. Don't know if that is a potential problem

Also, I think the car is missing the charcoal canister filter. Would that lead to this problem - or a vapor lock problem?

 

The spring should go in first then the filter. The hole in the filter should be towards the front so you can see it.