running bad, please help!

[dropanddrag71]

70 Chevy, SBC, automatic...
When I start it it runs nice, today it started bucking and bearly ran after 30 minutes or so.
Stuck on the side of the road, I hadda turn the idal screw all the way just to keep it from stalling to make it home. Once home I turn it off, restart it and it,s screaming the ideal is so high, I lower it and it goes from running nice to bucking, to running nice again. It has a clear fuel filter and it's full.
6 months ago it was the same thing, shop installed a new Msd streetfire, did a rewire, correctly and now it's back. All I can think of is a bad fuel pump or Carb.... any ideas?

[SS Tim]

Did you check for a vacuum leak?

[dropanddrag71]

I did look around, but isn't there a method of spraying a fluid on the lines and it will either speed up or stall?

**** I should mention that my truck has a manual choke and there IS NO cable attached to the Carb... wondering if the choke can be moving cause there no cable holding it n place...

[MidLifer]

If you spray Brakleen around vacuum fittings and lines, and you have a leak, it should speed the idle up temporarily. Carb cleaner will also work iirc.

[Shyguy]

If you have a manual choke you have to make sure it stays open. We used a piece of coat hanger to hold the one open on my '67, it was easy to do and is not noticable.

Check all the rubber hoses in the fuel line. There is one on the suction side of the fuel pump and one under the cab. The one on the suction side of the fuel pump was collapsing on one of my trucks. The sock on the suction of the fuel line in the tank was collapsing and causing problems on another truck.

[dropanddrag71]

Originally Posted by Shyguy

If you have a manual choke you have to make sure it stays open. We used a piece of coat hanger to hold the one open on my '67, it was easy to do and is not noticable.

Check all the rubber hoses in the fuel line. There is one on the suction side of the fuel pump and one under the cab. The one on the suction side of the fuel pump was collapsing on one of my trucks. The sock on the suction of the fuel line in the tank was collapsing and causing problems on another truck.

If it was a bad line or sock, would the clear fuel filter be empty? It's full now and always

Can the choke open and close while driving with no cable attached to it

[1972_Buford]

Fuel sock maybe? clogging the line?

[SS Tim]

Have you diagnosed a fuel delivery problem or just changing parts and hoping your drivability problem goes away?

[don t. - 72gmc]

Originally Posted by dropanddrag71

70 Chevy, SBC, automatic...
When I start it it runs nice, today it started bucking and bearly ran after 30 minutes or so.

When it dies, check for spark at a plug.

HTH...don t. ....

[dropanddrag71]

Originally Posted by SS Tim

Have you diagnosed a fuel delivery problem or just changing parts and hoping your drivability problem goes away?

I am no machanic, so I am trieing to solve this...
Today I got up and noticed the air cleaner was dirty, changed it, also found a spark plug was very, very loose, redid that, then undid the gas cap some, allowing it to vent better.
Drove fine all day, bit I still don't trust it yet more then a few miles from home

[cdowns]

does this have a ponts distributor? cleaning points and setting the gap or dwell is good to do
cleaning and gapping the sparkplugs is good to do

changing the fuel filter inside the carb inlet is a good thing to do

if this has been sitting for any length of time a gas cleaner in the gastank is good//i like berrymans gas treatment available pretty cheap at walmart some guys like seafoam

a service manual is good for peeps of all ages

[ole dollor]

is your motor a v-8 with a four bbl carb, some times the back butterflies will hang open and that will make one run real bad, check your carb and make sure they close all the way. you should be able to spray down in the carb and spray on the outside and clean it up, flop the back butterflies open sever times and do this with the motor OFF. let it set a few minutes and crank her up and see how she runs...good luck on the truck.

[dropanddrag71]

Originally Posted by cdowns

does this have a ponts distributor? cleaning points and setting the gap or dwell is good to do
cleaning and gapping the sparkplugs is good to do

changing the fuel filter inside the carb inlet is a good thing to do

if this has been sitting for any length of time a gas cleaner in the gastank is good//i like berrymans gas treatment available pretty cheap at walmart some guys like seafoam

a service manual is good for peeps of all ages

6 months ago I had a shop install a Msd street fire, wires, plugs etc.
Sitting?... this truck got a full restore in 2000, sat in his garage till summer 2012. I came along and I,m driving it and dealing with sitting issues

[GASoline71]

When the shop installed the HEI did they bypass the 12v "resistor" wire that was originally used on the points distributor?

The HEI needs a constant full 12v... not 12v with a resistor.

Also if it's the stock 40 year old Q-jet... it could need a throttle shaft rebush to prevent a wicked vacuum leak.

Gary