runs great, at first

[straitnate14]

ok ya thats a little bit sketchy I thought that you replaced all those things and then it started happening

[War Egil]

I had the same problem a couple of years ago. It turned out to be crud in the carb bowls. I took the Edelbrock apart and cleaned it, then put a new tank between the frame rails and haven't had that problem again.

[Indyuke]

Have you checked for plugged or partially plugged exhaust?

Tap a vacuum gauge into the manifold and see what it's reading. It should hold steady somewhere between 18"-21" Hg., no fluctuation or drops.

Does the truck start to die off while parked and running, or does it only do it while driving?

[bhoeger70]

I had a jeep that had the same thing going on thought it was fuel but finialy changed the plug wires and that took care of it

[straitnate14]

do you have a fuel pressure gauge? I just wounder if it sucks the carb dry and then it cant fill back up while running? I dont know anything about your carb I run holly and I am a newbie at tunning, It just sounds a lot like what happed to me it shut off, sounded like it wanted to start and I could get it to run just not enough to drive it, replaced the fuel pump on the side of the road and it didnt help, towed it home, next morning it fired right up ran great for about a half an hour then it started running like crap, until it died then I checked spark and it was very jumpy like it would spark a few times then stop sparking for like 30seconds replaced the module and it ran great.

[2bits]

I thought vacuum at first myself but really with a major or even minor vaccum leak you would see the problem at low speed and idle, at WOT an other higher speeds, there is little vaccum existing anyway.

As far as the choke is concerned, flop the butterfly plate on top around, see what linkage is involved, and zip tie it redneck style to where they are forced open. Obviously this is not the solution, just a troubleshooting step to see if it has anything to do with it. You can run it around the block and when it starts to mess up leave it running and take the air cleaner off and see if the butterfly is closed any, rev it up and feel it. then hold it open and rev it up again. That should be enough to tell you if it has anything to do with it. Mine did the same thing a I just disconnected the choke altogether and just babied the engine while it was cold for the first few miles while it heated up.

Could be the float level too, but I'm not feelin it yet since three miles is kind of a long way to drive before it goes dry.

[1970heavychevy]

I have cleaned the bowls in the carb. and blew cleaner through all the ports (I think all the ports). 2bits, are you thinking the choke is closing when I get down the street? I' m going to take the carb apart completely to clean and check everything. What do you think about an electric choke upgrade? Also the exhaust seems strong.

[Lobo'74]

Check the flat three wire harness on the distributor that runs from the module up to the coil. My truck would have problems with running without power and rough and would foul plugs. Get new module, change plugs and it would work for a month or two then start all over again. I finally got the shop manual and a multi meter out to check the ignition system. As I started the process I saw a little bit of copper showing through that harness. On closer inspection there were many small cracks through the insulation all over the underside of that harness. Wet weather allowed it to short out, kill the module and start the problem all over.

$20 part (special order) from the local Chevy dealer. Put it in along with a new module and plugs about two or three years ago - no problems since.

Check that small flat three wire harness on the dizzy . . .

[Lobo'74]

Or maybe its a four wire harness . . . Its the only flat wire harness that comes out the bottom of the distributor and goes up to the top, on the outside of the distributor.

[Somecallmejoe]

OK i have a question. Does it only have the problem under a load? Will the truck free rev if you are sitting in the driveway? If it's only happening under a load that will tell us more and we may be able to help you out more.

[1970heavychevy]

It happens when I'm driving, idle seems smooth. Keep in mind it works GREAT for the first 5 to 10 minutes. If it ran like that the whole time I would be very happy. But it feels like something is clogged in the carb. It even surges a little like it might brake free but never does. If I floor it, it gets worse. If I give lite throttle then it will at least get back home.

[Somecallmejoe]

I see you put in a regulator. Is it a fuel pressure regulator? If so what is your fuel pressure at? When it starts to run bad is it popping threw the carb or backfiring or anything? Is your fuel system all stock or do you have an electric fuel pump? Is your ignition stock? In 1970 i believe that truck should have had points in it. Sorry for all the questions. Just trying to help you narrow it down.

[1970heavychevy]

Edelbrock said to set regulator at about 5.5. If it's popping through the carb, it's not doing it at idle and I haven't noticed it while driving. It's a mechanical pump and the ignition is HEI. No problem with questions I just want it fixed. I want to drive it around town and have big plans for it.

[Somecallmejoe]

OK next questions. Did this just start happening one day or did you buy the truck this way? Is there a new power wire run to your HEI or is it hooked up to the factory resistance wire in the truck?

[Somecallmejoe]

Oh i thought of one more thing that might help. After you drive your truck and it acts up and you get it back home it would be helpful to know what the plugs look like. You should only need to pull one. If it's black and sooty its probably a rich condition or an ignition problem. If the plug is clean and looks new its probably a lean condition.

[1970heavychevy]

I bought the truck with the problem but I bought it from my dad. He bought the motor rebuilt 5 years ago, drove it for 2 until it started acting up. It happened out of nowhere. I ran a new power wire to the HEI. Its plugged into the back of the fuse box on the engine side. Also the plugs are clean after driving, tan color. I pulled the carb apart last night. I noticed it was sooty in side. I am cleaning and rebuilding it. When I reinstall it I will be installing a wire for the choke (it currently does not have one and the choke just sits there). I will also be putting the correct adapter on it. It has a square bore and Edelbrock recommends their spread bore.

[1970heavychevy]

[68350]

All of ours, we run the HEI power wire through the firewall into the fuse box. Is yours just plugged in right there on the firewall?

[68Stepbed]

My dad had a similar problem with his ElCamino a few months ago. It would start off running fine until the engine got warmed up, then it would sputter, then die. It wouldn't start back up and run until it cooled off. We checked everything we could think of. We narrowed down every possible problem and still couldn't figure it out. He had a new MSD Street Fire dist in the box for the engine for his 56 BelAire project. I mentioned trying the new dist. and he didn't think that would be the problem. I called a friend that's retired from GM and is an absolute gearhead guru. I asked him about the dist. being bad. He said to try the new one just see. We put in the new dist. and it ran great. It hasn't had any more problems either.

This problem was like yours. It just happened suddenly without warning.

[1970heavychevy]

Originally Posted by 68350

All of ours, we run the HEI power wire through the firewall into the fuse box. Is yours just plugged in right there on the firewall?

Yes. Where do I plug it into the fuse box?

[Somecallmejoe]

Here's something else to think about to. Even if you changed the ignition module you probably didn't change the pickup coil in the distributor. Usually they work or they don't.

[1970heavychevy]

I replaced the ignition coil.

[2bits]

Originally Posted by 1970heavychevy

I have cleaned the bowls in the carb. and blew cleaner through all the ports (I think all the ports). 2bits, are you thinking the choke is closing when I get down the street? I' m going to take the carb apart completely to clean and check everything. What do you think about an electric choke upgrade? Also the exhaust seems strong.

Yeah, sorry for the late reply, that's what I was thinkin of. Wire it open to be sure it isn't closing on you (even if it isn't hooked up, the airflow could pull it closed). That's my best guess. I don't use chokes at all.

[Longhorn321]

O.K. Here is my .02 Before you go tearing into the carb, you need to check the fuel pressure. Diagnostics first, repairs later. If you aren't getting enough fuel to the carb, it wont matter that everything in the carb is all shiny and new. I know you said you replaced most of the fuel system but what's buggin me is that you said the sock in the tank was replaced 3 years ago. If I got all the info right, that means you replaced it right around the time it started acting up. What I didn't see in any of your posts was why you replaced the sock. My truck has rust in the tank and it has caused me some trouble but not exactly the same as yours...it would run for quite a while and then run out of fuel and shut off completely....let it set for a few min. and I could go a few more miles. I fixed it the first time by simply replacing the filters. It did it again. The second time, I pulled the sock out and it was kinda ripped so I just took it off and threw it in the garbage. What I did notice tho (and the reason for the long post) is that the metal tube the sock was attached to was partially clogged...I cleaned it good and so far have had no more trouble.

[ChevLoRay]

I never did read which Edelbrock you have. Does it have a choke pull-off? If it does, and it doesn't open the choke up after it has warmed up, the choke may be staying partially closed, meaning it gets a little air through the choke but not enough. That could cause the stumble that you get after it has warmed up and explain why it runs well up to that point.