1972 c20 running problems

[thetucks]

I have a 1972 c20 that I picked up last week. it was setting in a barn for the past 7 years of its life. I had to replace the fuel tanks with a salvage yard swap and a new battery. she started up and idled fine, but when you push the accelerator it cut out and died. come to find out it was only firing on 4 cylinders. I replaced the spark plugs and tried it again. still only 4 cylinders. then I went back to the salvage yard and got an hei distributor and put it in. now it was running on all 8, but still cut out and died when pushing on the gas. so I bought a carb rebuild kit and rebuilt the carb. put it back on and it did the exact same thing. I eded up rebuilding it 3 more times with the same results. so I went back to the salvage yard and got another quadrajet carb just like the one I have. put it on just like it was and started it up. no more cutting out. took it for a test ride and it run great. that was yesterday. today I added powersteering to the truck. started it up and took off for a test ride. started cutting out as I drove. What do I do now? take the carb off and rebuild it? replace the fuel pump? any help would be great. thanks.

[WorkinLonghorn]

How is the idle ? ('It idled "fine" on 4 cylinders ?) Check for a vacuum leak first off. Check any diaphrams for leaks such as Brake booster (if equipped) etc. and all vac. lines,carb mounting too.
My truck had been sitting for years and the fuel pump didn't work at all after all that time. So yeah, test that. Test the plug wires if you have an ohm meter.

[thetucks]

I did check for vacuum leaks but I'm not sure if I did it right. I did not find any.
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[Mikey17]

Check your timing, are you getting fuel pressure? Stuck Heat riser maybe?

[PanelDeland]

Check any fuel filters also.Sometimes there's one between the tank and pump.There is also one in the inlet of the carb.Either may be passing enough fuel to idle without passing enough to run properly.Also take the line off the fuel pump and run a hose on the end of it.Put the hose in a jar and see what kind of fuel delivery you're getting.
Did you check the fuel sock on the fuel tank pickup?Sometimes they clog.

[thetucks]

I have good fuel pressure. I took the fuel line off the carb and put a hose on it and it sprays pretty good in pulses. is that what its suppose to do? I have replaced the fuel filter going into the the carb. I dont find any others. the sock on the fuel sender thats in the tank is actually gone. so its not stopped up.

I double checked the timing. I have it set at 8deg btdc. thats what the manual I have says. whats the heat riser? how do I check it?

The next thing I thought about doing was rebuilding this carb. I even though about replacing the spark plug wires. I hate to just keep replacing stuff.

[geezer#99]

Bump your timing up to 12 degrees. Make sure you plug the vacuum line to the distributor when you set it.
When you put in an hei did you run 12 volts to it?
Heat riser is a valve in your exhaust that's situated between your exhaust manifold and the exhaust pipe. It will be closed when you first start up. It's controlled with a coil. When the coil heats up the valve opens. It should only be closed when motor is cold. Maybe yours is stuck shut.

[thetucks]

ok ill bump it up to 12 deg btdc. I didnt know you have to plug the line to the distributor. which side do I plug? coming out the carb or out of the distributor? Im not sure if I even have the heat valve in my exhaust. ill have to check. thanks everyone.

[geezer#99]

Plug the vacuum line coming out of the carb. Pull it off at the distributor. A golf tee makes a good plug or a pencil.

[Mikey17]

Did you ever set your carb when you replaced it? float levels etc...

[no moa]

First thing that caught my attention was you swaped out the tank for another salvage yard tank. What did the tank look like inside?
Did you blow the lines out?
Why are you rebuilding the carb more than once? Did you do it right the first time? Does the carb keep gumming up? I have never rebuilt a carb more than once unless i did it wrong, or it got gummed up again.

[thetucks]

I havent rebuilt the carb thats on it now yet. im going to get a rebuild kit today and do that. the reason I rebuilt the other one so many times is because I wasnt for sure if I did something wrong or not. because it wasnt working. The original gas tank was very very very rusty inside. infact it has rusted 2 holes on the tank right at the level of the gas that was in it. the tank I got from the salvage was clean. I hooked a gas can full of gas to the lines of the truck and run it for a while before I put the new one on to make sure the lines were clean. at first it ran out pretty nasty stuff out the return line but now its clean gas. that was on the first carb that I did this.

[thetucks]

Could it possibly be I just need to adjust the timing to the 12deg btdc?

[Sport/Truck]

Originally Posted by thetucks

I did check for vacuum leaks but I'm not sure if I did it right. I did not find any.
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How did you check for leaks? Carb cleaner?
s/t

[thetucks]

I actually use starting fluid. Dan I took the line of of brake booster and checked it.
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[Sport/Truck]

Originally Posted by geezer#99

Bump your timing up to 12 degrees. Make sure you plug the vacuum line to the distributor when you set it.
When you put in an hei did you run 12 volts to it?
Heat riser is a valve in your exhaust that's situated between your exhaust manifold and the exhaust pipe. It will be closed when you first start up. It's controlled with a coil. When the coil heats up the valve opens. It should only be closed when motor is cold. Maybe yours is stuck shut.

Thetucks - did you check all of these?

[ls1nova71]

You say you replaced the fuel filter, but they're small and clog up easily. I have to replace mine every couple of weeks due to rust and junk in the tank. If you have no strained on the sender that makes it worse.
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[thetucks]

I will be checking all of these this morning. Does the engine have to be warmed up to set the timing?
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[thetucks]

ok heres the update: wow what a difference..... I started the truck and let it idle for a bit to warm it up. I pulled the vac line from the distributor and the truck died. I pluged the line and restarted it and it was running really really bad. I put the timing light on and checked it. it was at like 20deg after top dead center. so I loosened the dist. and turned it to 12deg btdc. I plugged the vac line back into the distributor and it is running so smooth. I took it for a test drive. it still had a little hesitation after I got moving until i picked up some speed. then it cleared. I drove it around town for a bit and it hardly does it at all now. it only does it when I stop then go to take off again. but not all the time and mostly when I push the accelerator easy to take off. sorry im rambling but Im trying to explain the best I can. one more thing. it may have nothing to do with it but when I go to stop if I push the brake pedal very soft and slow like I have to do on my 2009 silverado the peday goes way down to the floor. if I push it faster it dont go down very far. and it kinda seems like it the hesitation when taking off more when I push the brake soft to stop. im not sure if that even makes sense. again sorry for the long rambling. you guys have helped me so much already. I really appreciate it.

one more thing. I never found anything inline of my exhaust except the muffeler. I have stock manifolds to a single exhaust pipe.

[geezer#99]

It helps if it's warmed up a bit. Do one thing at a time. Adjust timing. Slow idle down then adjust idle mixture screws.
And like I asked before. Do you have 12 volts hooked to your distributor?
Brake problem is probably vac hose to the booster leaking or check valve stuck.
Heat riser valve will be on passenger side right where exhaust pipe hooks to the manifold.
Sounds like you you rebuilt your carb too many times when it was incorrect timing!!

[thetucks]

oh sorry, yes I ran a new wire directly from the distributor to the fuse box. ill turn the idle down and adjust the air mixture screws after lunch. I believe you start with either one and turn it in until engine goes down then back up and find a happy medium. then do the other screw it that right? do I then turn the idle back up? thanks

[thetucks]

I just saw you added to your last post. I have not rebuilt the carb at all that is on it now.
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[geezer#99]

True but you did rebuild the other one several times when it was just a timing issue.
Thing to remember is check the basics first. Sometimes there's a simple cure. Better than throwing a lot of time and money at it.

[thetucks]

Yes you are right. I did rebuild it too many times probably for no reason.
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[Sport/Truck]

Originally Posted by thetucks

one more thing. I never found anything inline of my exhaust except the muffeler. I have stock manifolds to a single exhaust pipe.

Most of the time they remove it. If it was on there it's mounted directly on the manifold's outlet on one side. Passenger side IIRC.