Truck is not running

[Kip7143]

Hi Guys!

I am hoping for some help with my 1981 Chev. Since I bought the truck it's been a little rough and tempermental but drivable for the most part. Now it's really not running. So here are some details.

The truck at this point is only running when throttle is held. As soon as I get off the throttle it chokes and dies. When it is running, its sputtering, almost like a misfire. Since I got the truck I knew a lot of the vacuum lines were old and cracked, so I recently replaced everything to see if that made a fix.

Still the truck isnt idling and will only run on throttle, with a good sputter. Does anyone have any idea where I should start? One thing, when I disconnect the vacuum from distributor it still runs very rough, but wont stall.

Second to all of this... I do not know how to time this truck. There doesn't seem to be a timing tab.. does anyone know how to time the straight six motors?

NOTE: the clip is from a 79, its not the factory clip on that truck

1981 Chev C10, straight 6 4.8l motor, Automatic. Pretty well all stock.

[sick472]

When you disconnect the vacuum line from the distributor, do you plug the line to keep that from being a vacuum leak?

Have you inspected the inside of the distributor cap for wear or contamination?

[Kip7143]

Yeah plugging the line yielded the same results. Im going to take the distributor apart today and check the EGR valve.

[geezer#99]

Do you have a pic of the engine bay?
Without the air cleaner on is best.

[Kip7143]

Here you are

[geezer#99]

The timing tab is at 10 o’clock.
Pic in post #15 shows it’s location.


http://67-72chevytrucks.com/vboard/s...d.php?t=702366

[jayoldschool]

Good info so far! Do you have a photo of the idle speed screw and throttle linkage?

[Dead Parrot]

If you have vacuum assist power brakes, a leaky booster can leak enough air to cause idle problems while still providing enough boost to make the brakes seem normal.

If the transmission has a vacuum shift modulator, make sure those vacuum hoses are good.

The vacuum pot on the distributor can leak as well. Might explain why the truck keeps running with the vacuum pot disconnected and the line plugged.

[Kip7143]

Hi all, thanks for the replies.

I did some work today and heres what I've come up with. I changed the majority of the distributor parts and found some heavily warn components. I will post pictures below.

I made the mistake of playing with a few things at one time, so I don't know what made the biggest impact. Reading my 1981 Chevy repair manual, in the diag section I found some info that an faulty EGR will present similar symptoms that I am seeing now, rough idle, stalling, sputtering. So I removed the EGR and did a bench test, when I first depressed the diaphragm and covered the vacuum port it didnt move back, I thought "oh this is good". Then I let go and it remained in the same place and thought "oh this may not be good". I continued to move the diaphragm until it moved freely.

I then pulled all the spark plugs but they were all in good shape and gapped appropriately. So I didn't find anything wrong there.

I put everything back together and its running a lot better. It's starting much easier, running smoother. I'm thinking the combination of fresh destributor parts and freeing up the EGR is what's making it run better. I am thinking of changing the EGR regardless.

The only issue currently is I cant adjust idle. The idle screw doesnt seem to want to sit properly for hot or cold adjustments. Its idling in park at about 1100 and in drive at 800.

The only symptom still perssisting, which has really always been there, is a randon sputter or popping at when idling in park. Any suggestions or comments?

[truckin 79]

I would check out a few spark plugs and see what they look like. They will tell you a lot, black they are rich, oily bad rings or seals and white and chalky could be lean. You could also get truck to idle and put hand over carb slightly, if it smooths out and RPM climbs it is running lean and possible vacuum leak, if it dies right away probably to rich. Just some simple checks also look for timing tab it might be covered in grease

[geezer#99]

You need to check the timing.
Your high idle in drive and park can be from a lack of initial timing.
Did you check the vac pot on the distributor too?

[Kip7143]

I did pull the plugs, they are white / chalky. Definitely a solid chance if a vacuum leak since most of the hoses were super old and original.

I think the timing tab was knocked off the truck or something. I’ve had others look and no one can find it in either the 10 or 2 position. I checked with a timing light today and cyl 1 is TDC around the 10 o’clock position.

[geezer#99]

You could make your own timing tab or adapt one like this.
You’d need to find true tdc using a piston stop.

https://www.holley.com/products/engi...ape/parts/4597

[Kip7143]

Hi again,

Got the truck running and driving but it’s still dying at idle randomly. It’s definitely running rich, you can smell it and see the white on the plugs.

Now one thing I’m having trouble with is low idle. I took a photo of the idle screw and the 3 step piece it’s supposed to touch. When the choke turns off, the idle screw sits below the lowest level so I can’t adjust the idle speed. Anyone experience this? I’ll attach a couple of pictures for reference.

[Corts60]

Having white plugs and a rich condition at the same time doesn’t really add up. Plugs should be black if you’re smelling rich fuel. It sounds like that carb needs to come off and be gone through. All these problems you’re reporting, you may just have a gummed up idle circuit or something like that. Also, are you sure that screw you took a picture of is not the fast idle screw? That is different from the regular idle adjustment.

And that screw is stripped bad. Maybe time for a whole new carb?

[Kip7143]

Originally Posted by Corts60

Having white plugs and a rich condition at the same time doesn’t really add up. Plugs should be black if you’re smelling rich fuel. It sounds like that carb needs to come off and be gone through. All these problems you’re reporting, you may just have a gummed up idle circuit or something like that. Also, are you sure that screw you took a picture of is not the fast idle screw? That is different from the regular idle adjustment.

And that screw is stripped bad. Maybe time for a whole new carb?

Is there a different “idle speed screw” elsewhere? That’s the only one I can find.

[Pontiac1976]

It's normally near the base of the carb you should see only the head of the screw mostly

[Kip7143]

Could this be it? Doesn’t seem to make contact with the throttle?

Cool to see you’re in Ottawa! I have an old Pontiac too!

[Corts60]

I’m not familiar with your style carburetor, but my guess is that screw in the background with a spring on it is the idle adjustment. The other one is definitely a fast idle adjustment or it wouldn’t be on a stepped cam like that.

[Kip7143]

Okay thanks .. I’ll play around with it and see what I can get

[Pontiac1976]

I'm guessing the back one is the butter fly adjustment. Does the carb have a name it does look like Rochester, but should be lower part of the carb near the front or front side It might be sealed off or have a plug over it if it never been rebuilt.

[Corts60]

Originally Posted by Pontiac1976

I'm guessing the back one is the butter fly adjustment. Does the carb have a name it does look like Rochester, but should be lower part of the carb near the front or front side It might be sealed off or have a plug over it if it never been rebuilt.

I think you’re talking about the idle/air adjustment whereas I believe the OP is asking for the idle rpm adjustment.

[jayoldschool]

What is the actual make/model of this carb?

[Shugalou]

have you checked the carb to intake manifold isn't leaking by spraying some carb cleaner? I was having a ruff runner and die when cold and my carb bolts needed to be tightened...nice easy fix.

[DLH]

vacuum leak will cause high and rough idle. Get a can of carb cleaner and spray around the intake and carb mounting gaskets. Idle will change if you find a leak.