Rough idle and takeoff 250 inline

[68gmcdude]

Engine is idling worse and is getting worse under load. I advanced running to 8⁰ from 6⁰ and then increased to 10⁰. No improvement. I took the belt off of the smog pump so it wouldn't run and nothing improved. The carb has a nice stream of gas shooting into the carb when I pump the accelerator. I'm thinking the old truck didn't like the long 400 mile trip on the highway. I had never driven it that far in the highway before.
I'm going to do a compression check next. Any other suggestions? I'm thinking it's just tied and needs rebuilt at this point. Only 56k miles on it.

[Steeveedee]

C'mon people, there has to be someone local to him who can sort this out!

['68OrangeSunshine]

68gmcdude -- They sell little brass plugs that thread into your head to seal off any leakage from an inactive A.I.R. system. Also the steel tubing, pump, and bracket are dead weight now. It never did much to improve air quality. It just had the _appearance of doing something positive_ about air pollution. They were political, not engineering, ''improvements.''
I appreciate your desire to keep the truck original.
At only 56,000 your rings should still be tight. L6s are bombproof.
I ran my second 292 L6 to 250,000 -- by then I was blowing big blue smoke rings of Valvoline 50 weight.
Do the compression check, and get back to us.
Good luck.

[68gmcdude]

Originally Posted by '68OrangeSunshine

68gmcdude -- They sell little brass plugs that thread into your head to seal off any leakage from an inactive A.I.R. system. Also the steel tubimg, the pump, and bracket are dead weight now. It never did much to improve air quality. It just had the _appearance of doing something positive_ about air pollution. They were political, not engineering, ''improvements.''
I appreciate your desire to keep the truck original.
At only 56,000 your rings should still be tight. L6s are bombproof.
I ran my second 292 L6 to 250,000 -- by then I was blowing big blue smoke rings of Valvoline 50 weight.
Do the compression check, and get back to us.
Good luck.

Where are the brass plugs available that seal off the holes in the head?

[Steeveedee]

Air pollution arguments notwithstanding, we'll need to see a picture of your engine to determine the type of plug you need after the remove the AIR injection manifold. The threads are straight pipe with a shape of double flare 5/16" b-nut like a brake line fitting. I'll go on record right here with stating that the AIR system on any vehicle produced with it did not cause rough idle or take off. I'd like to hear credible stories of people who had this problem. Millions of vehicles were produced across ALL vehicle manufacturer's products where no complaints were lodged. I worked on those vehicles back in the day as a certified mechanic, and this was not an established issue, ever.

[68gmcdude]

Originally Posted by Steeveedee

Air pollution arguments notwithstanding, we'll need to see a picture of your engine to determine the type of plug you need after the remove the AIR injection manifold. The threads are straight pipe with a shape of double flare 5/16" b-nut like a brake line fitting. I'll go on record right here with stating that the AIR system on any vehicle produced with it did not cause rough idle or take off. I'd like to hear credible stories of people who had this problem. Millions of vehicles were produced across ALL vehicle manufacturer's products where no complaints were lodged. I worked on those vehicles back in the day as a certified mechanic, and this was not an established issue, ever.

Here is a pic of the fitting for the tube.

['68OrangeSunshine]

Originally Posted by 68gmcdude

Where are the brass plugs available that seal off the holes in the head?

I haven't needed them in decades, but I'll research it. On one head, I got a brass set from the local Hot Rod shop. Another head, I found set screws the right diameter and pitch.
I'll look around. Roughly about 3/8'' IRC.

['68OrangeSunshine]

Originally Posted by 68gmcdude

Where are the brass plugs available that seal off the holes in the head?

I asked at Don's Hot Rod Equipment in Tucson, but you should be able to get these anywhere:
Cornet....3/8 - Inverted Flange Plugs...p/n: 106-6....$1.60 [each] x 6 =$9.60

Prices may vary nationally. Other manufacturers may offer similar products with different prices and quality.

[68gmcdude]

Originally Posted by '68OrangeSunshine

I asked at Don's Hot Rod Equipment in Tucson, but you should be able to get these anywhere:
Cornet....3/8 - Inverted Flange Plugs...p/n: 106-6....$1.60 [each] x 6 =$9.60

Prices may vary nationally. Other manufacturers may offer similar products with different prices and quality.

Thank you!

[geezer#99]

Redo the lifter adjustment.
Only do 1/4 turn from zero lash.

[68gmcdude]

Originally Posted by geezer#99

Redo the lifter adjustment.
Only do 1/4 turn from zero lash.

I was thinking this as well. Maybe the three 1/4 turns I did was too much?

[Dashman]

You said you were missing the spring behind the fuel filter, correct? That would mean the gasketed side of the filter wasn't sealing to the surface of the inlet nut. How long was it like that for? I think you got some debris passed the fuel filter, and into the carburetor. ...something into the idle circuit or primary circuit.

[68gmcdude]

Originally Posted by Dashman

You said you were missing the spring behind the fuel filter, correct? That would mean the gasketed side of the filter wasn't sealing to the surface of the inlet nut. How long was it like that for? I think you got some debris passed the fuel filter, and into the carburetor. ...something into the idle circuit or primary circuit.

Since I discovered that, the carb has been taken apart, thoroughly cleaned and reassembled with new gaskets, springs, accelerator cup, etc. The spring is now in the filter port with a new filter. Carb shoots a nice flow of gas now when the accelerator is pumped.

[howzzzit]

When you changed the condenser and points did you use a reputable brand?

[68gmcdude]

Originally Posted by geezer#99

Redo the lifter adjustment.
Only do 1/4 turn from zero lash.

I readjusted the valves and set them a 1/4 turn from zero lash. When I did a 1/2 turn it was still idling a little rough. I did this with the engine running. The idle is smooth now. Before I put the valve cover back on, I'm going to let it sit overnight and start it again tomorrow to see if it's still ok.
So are the 1/4, 1/2 and 3/4 turns on a valve adjustment simply recommendations and each motor is different? I originally did a 3/4 turn on each valve.

[Rust_never_sleeps]

Originally Posted by 68gmcdude

I readjusted the valves and set them a 1/4 turn from zero lash. When I did a 1/2 turn it was still idling a little rough. I did this with the engine running. The idle is smooth now. Before I put the valve cover back on, I'm going to let it sit overnight and start it again tomorrow to see if it's still ok.
So are the 1/4, 1/2 and 3/4 turns on a valve adjustment simply recommendations and each motor is different? I originally did a 3/4 turn on each valve.

The book says preload is 1 turn from zero lash for everything from 250-427
For SBC the consensus seems to be 1/2 or 3/4 turn, but for a battleworn six, I'd guess you're going to know better than anyone else where it's happiest

[68gmcdude]

Originally Posted by Rust_never_sleeps

The book says preload is 1 turn from zero lash for everything from 250-427
For SBC the consensus seems to be 1/2 or 3/4 turn, but for a battleworn six, I'd guess you're going to know better than anyone else where it's happiest

When I adjusted them the first time, I tried the one full turn like the shop manual said, but the motor really didn't like, it barely kept running, so I ended up doing 3/4 turn. At the time it seemed ok. When I readjusted last night, it didn't like the 3/4 turn, so I tried a 1/2 turn and it was still idling rough. I backed it off to 1/4 turn and it idled good. Gonna go back out there this evening, start it up, let it run and see how it goes. If all seems good, the valve cover is going on and I'll take a test drive.... We'll see.

[68gmcdude]

UPDATE:

I did a compression test on the cylinders. Here are the results...
#1 - 160
#2 - 165
#3 - 165
#4 - 165
#5 - 65
#6 - 160

Another thing to note. All of the valves were backed off and tightened 1/4 turn, except the fourth valve from the rear, which I believe is the exhaust valve for cylinder number 5. That one needed to be tightened almost two full turns before the lash would go away. I'm guessing something is going on right there.

What does this mean and what are my next steps?

[geezer#99]

If you’re setting the valves, make sure to check all the rockers are moving the same amount.

[68gmcdude]

Originally Posted by geezer#99

If you’re setting the valves, make sure to check all the rockers are moving the same amount.

Will do. Plan on doing that after work tonight.

[Rust_never_sleeps]

Maybe check that the points condenser is healthy with a multimeter. I know it's new, but chaotic timing and backfires might be caused by a dying one

[68gmcdude]

Originally Posted by Rust_never_sleeps

Maybe check that the points condenser is healthy with a multimeter. I know it's new, but chaotic timing and backfires might be caused by a dying one

I will check that. I also have another condenser I can try putting on.

['68OrangeSunshine]

Cut-Out Valve Cover. That's a Pro move!

[68gmcdude]

Originally Posted by '68OrangeSunshine

Cut-Out Valve Cover. That's a Pro move!

My buddy had one laying around. Makes a nice splash guard.

['68OrangeSunshine]

Originally Posted by 68gmcdude

My buddy had one laying around. Makes a nice splash guard.

Especially as the little spoon clips they sell for adjusting V8 heads just wobble off L6 rocker arms. I have an old valve cover to use iike that, too.