Why is my engine choking out?

Naturally aspirated carburetor with automatic choke.

If youre in winter (northern hemisphere) then the choke will set when you depress accelerator for cold start.

After the engine starts it unloads (opens) the choke slightly. As the engine warms it continues to open the choke until fully open.

Likely the choke is not opening as the engine reaches normal operating temperature and fuel mixture us too rich causing poor combustion and black smoke.

check fuel pressure possible fuel pump issue

It sounds like it is getting too much fuel. check your fuel sensor. Your choke is sticking open. Buy some carb cleaner. Remove your air filter and spray the linkage to clean it up. Make sure it moves easy. Start your car up. the butter fly on top of the carb will be closed all the way. As the motor warms up this should open up gradually. If it doesn't you have a problem with the choke system and it is not letting air in as the motor warms up.

Did you replace the fuel filter also? Have fuel pressure checked, new pump does not always equal good pump, have gotten bad ones before. Check / replace gas cap- may not be holding correct pressure in tank. Or, the seal on the fuel pump hole may not have sealed. Occasionally, the choking and sputtering as well as a pop or hesitation can be caused by a bad catalytic converter. If the converter is plugged, it will choke your engine out due to back compression. A 1991 car with a rusted muffler would prompt me to check out the converter as it is most likely bad also and could be the root cause of your problem. Good exhaust is essential to good performance.

egr valve is bad

That would be a Holley, probably model 4160 carb on it. You need to do a little detective work on this. You either need to adjust the choke or find out where the fuel is going after 12 hours.

First, when the engine is running check the Intake and Carburetor gaskets for vacuum leaks. Also spray by the Vacuum reserve canister (Like a coffee can) with either Choke cleaner or a water mist. Either way the RPM will change if you have a Vacuum leak. Fix the vacuum leak if you find one. The engine needs Vacuum to draw in the fuel for a cold start. There are vacuum ports with gaskets (Hidden until disassembled) where the Choke housing attaches to the main block of the Carburetor. A leak here will mess up the tiny piston inside the Choke. (Its under the Black cover and operates the stepup for cold starts).

The black choke dial should be set for 2 marks rich. You should not need excess force on the choke flap to unload it. The choke flap should maintain an opening about 2 credit cards thick measured between flap and carb housing. To get this space you bend the rod pushing the choke flap. This should help the choke work better.

If this does not help, on the next 12 hour interval check for fuel by taking off the strainer on the Carb inlet and remove the line from the carb to the pump. If the fuel line is dry you are losing the Prime to the pump. You must have either a bad pump or a hole in the fuel line from the tank.

Would like to know what you found. The Power pump inside the front bowl of your Holley has a number and you can go to a Holley website to see if it is correct for your truck. The fuel inside the front bowl of your Holley should be enough start the truck. Even if the bowl went dry overnight, the fuel pump would replenish the supply well before 20 to 50 pumps.

full choke when starting
3/4 choke upon engine firing
open choke within 2 minutes

Start with the simple and replace the fuel filter. The fuel filter may have reached the end of it's life time and is dirty causing the issues you have. The worst is the fuel pump it self has gone bad and needs to be replaced, the fuel pump should be producing 62 to 65 PSI when the engine is started and should drop no more then 5 PSI when the engine is running. You can check the fuel pressure at the shredder valve with a fuel pressure gauge. Good luck and keep me posted, be glad to help get your Yukon running 100% again.

One problem is related to the other.The dieseling is caused by a rich air/fuel mixture which is caused by the closing choke.So you need to adjust the choke to where it is slightly open when the engine is cold.If it is electric then it has a thermostatic device that positions the choke just cracked open when cold and slowly opens as the engine heats up.Whats happening is the choke may actually be loose and when the engine shuts off the vacuum pulls the choke close creating the combustable rich fuel mixture(if you watched the choke when someone else turns off the engine you'll see the choke flapping while the engine is dieseling).Try putting a screw driver in the carb(with engine running) blocking the choke from closing.Then shut the engine off.It shouldnt diesel.You may have to replace the carb thermostat

first you have to check for code with scanner , sounds like you have sensor problem , (coolant temp sensor map sensor etc). it could be a fuel delivery issue like lean condition . but the code for engine light will guide you in right direction. good luck